Table of Contents

• The latest news from ruby-lang.org
• Installation
  • Troubleshooting
    • macOS
  • How to install Ruby
  • How to install ruby gem manager, bundler gem
  • What is a Gemfile and Gemfile.lock
  • How to install a specific version of a particular ruby gem
  • How to update a single gem using Bundler
  • How to update every gem in the Gemfile using Bundler
• Introduction
• Reserved Words
• Comment
• Operators
• Variables and Scope
  • Pseudo variables
  • Pre-defined variables
  • Pre-defined global constants
  • How to check scope of variables
• Conditional structures
  • If elsif else expression
  • unless expression
  • Shorthand
  • Case Expressions
• Data types
  • How to check the data type
• Symbol
• String
  • How to convert String to lower or upper case
  • Helpful methods
• Integer
  • Helpful methods
• Range
  • Helpful methods
  • How to use step with Range
• Methods
  • How to declare a method
  • How to call a method
  • How to define a default value for a method parameter
  • How to use another parameter for the default value
  • How to pass variable length argument to a method parameter
  • Modify object
  • Boolean method
  • Class method
• Blocks
  • How to check if a block is given
• Procs
• Lambdas
• Blocks VS Procs VS Lambdas
• Array
  • How to iterate an Array
    • each
    • each_with_index
    • each_with_object
    • each_index
    • map
    • collect
    • while
    • do while
    • for
    • until
    • times
    • upto
    • downto
    • step
    • inject
    • reduce
    • detect
    • find
    • select
    • reject
    • keep_if
    • delete_if
    • drop_while
  • Boolean Enumerable methods
    • all?
    • any?
    • one?
    • none?
    • empty?
  • How to check if a value exists in an Array (include?)
  • How to get array size
  • How to clear an Array
  • How to get the first element of an Array
  • How to get the last element of an Array
  • How to merge two Arrays
  • How to sort an Array
  • How to get the maximum from an Array
  • How to get Array elements using a range
  • How to get first n elements of an Array
  • How to access an element
  • How to remove one or more elements of an Array
  • How to remove duplicate elements from an Array
• Hash
  • How to group by count
  • What's the difference between Hash.new(0) and {}
  • How to sort a Hash
  • How to get the maximum from a Hash
• Loop
  • How to break out from loop
  • How to skip inside a loop
  • How to repeat the current iteration
  • How to restart a loop
• Classes
  • How to inherit a class
  • How to check instance type
  • Print all method names of a class
  • Check if a Class has a particular method
• Modules
• Operator Overloading
• Exception Handling
• Regular expression
• Miscellaneous
  • How to generate random number
  • Check the syntax of a Ruby file
  • Concatenate String in a loop
  • CamelCase String split
  • Ruby scripts
• Platforms that supports Ruby
• Ruby frameworks
• My Ruby Articles
• Books and other resources
• Bug Reports and Feature Requests
• Contribution Guidelines
• Author
• License

The latest news from ruby-lang.org

• Ruby 3.1.2 Released
  _{2022-04-12 12:00:00}
• Ruby 3.0.4 Released
  _{2022-04-12 12:00:00}
• Ruby 2.7.6 Released
  _{2022-04-12 12:00:00}
• Ruby 2.6.10 Released
  _{2022-04-12 12:00:00}
• CVE-2022-28738: Double free in Regexp compilation
  _{2022-04-12 12:00:00}
• CVE-2022-28739: Buffer overrun in String-to-Float conversion
  _{2022-04-12 12:00:00}
• Ruby 3.2.0 Preview 1 Released
  _{2022-04-03 00:00:00}
• Ruby 3.1.1 Released
  _{2022-02-18 12:00:00}
• Ruby 3.1.0 Released
  _{2021-12-25 00:00:00}
• Ruby 3.0.3 Released
  _{2021-11-24 12:00:00}

Installation

Troubleshooting

macOS

macOS Big Sur (Version 11.3)

List all the installed Ruby versions:

which -a ruby
# /usr/bin/ruby

Get information about currently used Ruby:

ruby -v
# ruby 2.6.3p62 (2019-04-16 revision 67580) [universal.arm64e-darwin20]
gem env

How to install Ruby

First things first, make sure you have Ruby installed on your machine. In case you don’t want to install Ruby natively, you can use docker.

docker run -it --rm ruby:latest
# check which version of Ruby you're running
RUBY_VERSION

Run a specific version of Ruby.

docker run -it --rm ruby:2.7
# check which version of Ruby you're running
RUBY_VERSION

RVM

\curl -sSL https://get.rvm.io | bash -s stable
rvm list
rvm install 3.0.1
rvm install 3.0.0
rvm list
rvm use 3.0.1

How to install ruby gem manager, bundler gem

# access the bash for executing the following commands
docker run -it --rm ruby:latest bash

gem install bundler
bundle -v
gem update bundler
gem uninstall bundler

Further reading

What is a Gemfile and Gemfile.lock

Gemfile is a configuration file for Bundler (also a gem), which contains a list of gems for your project (dependencies).

Further reading

# specify your gems in a Gemfile in your project’s root
ruby '2.5.6'

source 'https://rubygems.org'
gem 'nokogiri'
gem 'rack', '~>1.1'
gem 'rspec', :require => 'spec'

# install all the gems in the Gemfile
bundle install

How to install a specific version of a particular ruby gem

gem install bundler -v 1.17
gem install minitest -v 5.8.4

How to update a single gem using Bundler

bundle update nokogiri

Bundler attempted to update gem_name but its version stayed the same.

1. Another gem depends on the gem_name.
2. The version number is specified in your Gemfile for gem_name.

'gem_name', '~> 2.0.5'

How to update every gem in the Gemfile using Bundler

bundle update

Introduction

Ruby is a pure object-oriented and interpreted (executes the code at runtime) programming language invented in the mid-90s by Yukihiro Matsumoto. In Ruby, everything is an object. It is easy to learn with dynamic typing and automatic memory management.

With the idea that programming should be enjoyable for programmers, it was created to increase programmer productivity. It emphasizes the necessity for software to be understood by humans first and computers second.

Ruby will be quite familiar to Python, and Perl developers (and to a lesser extent C# and JavaScript developers) as Ruby was heavily inspired by Perl in certain areas (as was Python). Ruby is less related to languages like C, C++, or Java because these languages are compiled (not interpreted), statically typed, and focused on performance rather than flexibility and conciseness.

Ruby comes with a program that will show the results of any Ruby statements you feed it. Playing with Ruby code in interactive sessions like this is a terrific way to learn the language.

Open up IRB (which stands for Interactive Ruby).

• If you’re using macOS open up Terminal and type irb, then hit enter.
• If you’re using Linux, open up a shell and type irb and hit enter.
• If you’re using Windows, open Interactive Ruby from the Ruby section of your Start Menu.

1.next # 2

To test the above code, type the irb command from your shell to initiate the interpreter.

Reserved Words

__ENCODING__ , __LINE__ , __FILE__ , BEGIN , END , alias , and , begin , break , case , class ,
def , defined? , do , else , elsif , end , ensure , false , for , if , in , module , next , nil ,
not , or , redo, rescue , retry , return , self , super , then , true , undef , unless , until ,
when , while , yield

Further reading

Comment

# single line comment

=begin
multiline
comment
=end

I prefer # for multiline comments because it maintains my style guide and is easier to read.

Operators

Variables and Scope

There are five different types of variables. The first character determines the scope.

1. Scope of a local variable is one of

proc{ ... }
loop{ ... }
def ... end
class ... end
module ... end
the entire program (unless one of the above applies)

2. Scope of an instance variable is

Instance variables cannot be altered except for some methods, and it's distinct to each object of a class.

3. Scope of a class variable is one of

It can be called from a class by calling ClassName.class_variable, and it's independent of any object of a class.

4. Scope of a global variable is

It can be referred from anywhere in a program.

5. Scope of a constant variable is

Accessible outside the class.

Pseudo variables

Pre-defined variables

Option variables: The variables which names are in the form of $-?, where ? is the option character, are called option variables and contains the information about interpreter command line options.

Source

Pre-defined global constants

Source

How to check scope of variables

defined? count
"local-variable"
defined? @id
"instance-variable"
defined? @@name
"class variable"
defined? $version
"global-variable"
defined? PI
"constant"

Conditional structures

If elsif else expression

temp = 19

if temp >= 25
    puts "hot"
elsif temp < 25 && temp >= 18
    puts "normal"
else
    puts "cold"
end

# output
# normal

unless expression

# The unless is opposite of if, evaluates when the statement is false

name = "rob"

# if name != "bob"
unless name == "bob"
    puts "hello stranger"
else
    puts "hello bob"
end

# output
# hello stranger

Shorthand

count = 1
puts "hello world" if count == 1
# output
# hello world

count = 2
puts "hello universe" if count != 1
# or using unless
puts "hello universe" unless count == 1
# output
# hello universe

Case Expressions

# case returns the value of the last expression executed

case input
# check an integer, 19
when 19
puts "It's 19"
# check a float number, 33.3
when 33.3
puts "It's 33.3"
# check an exact string, "Zaman"
when "Zaman"
puts "Hi Zaman"
when 10
puts "It's 10"
# check against a range
when 7..11
puts "It's between 7 and 11"
# check against multiple values, "coffee"
when "tea", "coffee"
puts "Happy days"
# check against a regular expression, "aA6"
when /^a[A-Z]+[0-6]+$/
puts "It's a valid match"
# check any string by comparing against the String class, "any string"
when String
puts "It's a String"
end

# using short syntax
case input
when 19 then puts "It's 19"
end

# optional fallthrough
case input
when 19 then puts "It's 19"
else
puts "It's not 19"
end

# get the return value
marks = 86

result = case marks
    when 0..49 then "Fail"
    when 50..64 then "Pass"
    when 65..74 then "Credit"
    when 75..84 then "Distinction"
    when 85..100 then "High Distinction"
    else "Invalid marks"
end

puts result
# High Distinction

Data types

Further readings

How to check the data type

# both are synonymous
a = 37
a.kind_of? Integer
# true
a.is_a? Integer
# true

Symbol

Symbol objects represent names. Symbols are immutable, which means every symbol is unique, and we can't change it. Referencing the same symbol multiple times is the same as referencing the same object everywhere in your program. As a result, we can save both time and memory by referencing the same memory location.

Symbols as hash keys.

week_days = {sunday: 11, monday: 222}

String

How to convert String to lower or upper case

Helpful methods

Integer

Helpful methods

2.even?
# true
3.even?
# false

Range

Ranges allow us to declare data with a beginning and an end, it has two operators to generate ranges.

# .. for creating inclusive ranges

range = 1..10
range.to_a
# output
# [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

# ... for creating exclusive ranges

range = 1...10
range.to_a
# output
# [1, 2, 3, 4, 5, 6, 7, 8, 9]

Helpful methods

How to use step with Range

(1..20).step(2) { |number| puts "#{number}"}
# output
# 1
# 3
# 5
# 7
# 9
# 11
# 13
# 15
# 17
# 19

Methods

A method is a function that takes zero or more parameters and returns a value. Ruby method returns nil by default.

How to declare a method

In Ruby, the last statement evaluated is the return value of that method. The return statement is optional. Depending on your preference, you can choose either of them 👍. I prefer to use the return statement because it's easier to understand.

def method_name(parameter1, parameter2)
    puts "#{parameter1} #{parameter2}"
    parameter1 + parameter2
end

res = method_name(20, 10)
# output
# 30

def method_name(parameter1, parameter2)
    puts "#{parameter1} #{parameter2}"
    return parameter1 + parameter2
end
# output
# 30

How to call a method

res = method_name(parameter1, parameter2)
# In Ruby you can call methods without parentheses
res = method_name parameter1, parameter2

How to define a default value for a method parameter

def method_name(parameter1, parameter2, type = "ADD")
    puts "#{parameter1} #{parameter2}"
    return parameter1 + parameter2 if type == "ADD"
    return parameter1 - parameter2 if type == "SUB"
end

res = method_name(20, 10)
# output
# 30

How to use another parameter for the default value

def method_name(num1, num2 = num1)
    return num1 + num2
end

res = method_name(10)
# output
# 20

How to pass variable length argument to a method parameter

def method_name(type, *values)
    return values.reduce(:+) if type == "ADD"
    return values.reduce(:-) if type == "SUB"
end

numbers = [2, 2, 2, 3, 3, 3]

res = method_name("ADD", *numbers)
# output
# 15

res = method_name("SUB", *numbers)
# output
# -11

# or you can provide the values like this
res = method_name("ADD", 2, 2, 2, 3, 3, 3)
# output
# 15

Modify object

The ! is used after the method when you want to modify the object.

a = ["Drama",
"Mystery",
"Crime",
"Sci-fi",
"Disaster",
"Thriller"]
a.sort
puts a
# we didn't modify the object
# Drama
# Mystery
# Crime
# Sci-fi
# Disaster
# Thriller

a.sort!
puts a
# modify the object
# Crime
# Disaster
# Drama
# Mystery
# Sci-fi
# Thriller

Boolean method

In ruby methods that end with a question mark (?) are called boolean methods, which either returns true or false.

"some text".nil?
# false
nil.nil?
# true

You can have your own boolean methods.

def is_vowel?(char)
    ['a','e','i','o','u'].include? char
end

is_vowel? 'a'
# true
is_vowel? 'b'
# false

Class method

A class method is a class-level method. There are multiple ways of defining a class method.

class Mobile
    def self.ring
        "ring ring ring..."
    end
end

Mobile.ring

class Mobile
    def Mobile.ring
        "ring ring ring..."
    end
end

Mobile.ring

class Mobile
    class << self
    def ring
        "ring ring ring..."
       end
    end
end

Mobile.ring

A class method is an instance method of the class object. When a new class is created, an object of type Class is initialized and assigned to a global constant (Mobile in this case).

Mobile = Class.new do
    def self.ring
        "ring ring ring..."
    end
end

Mobile.ring

Mobile = Class.new

class << Mobile
    def ring
        "ring ring ring..."
    end
end

Mobile.ring

Blocks

Codes between do and end (for multiline) or curly brackets { and } (for a single line) are called blocks, and they can have multiple arguments defined between two pipes (|arg1, arg2|). A block can be passed as a method parameter or can be associated with a method call. A block returns the last evaluated statement.

# return value
def give_me_data
    data = yield
    puts "data = #{data}"
end

give_me_data { "Big data" }

# output
# data = Big data

# single line block
salary = [399, 234, 566, 533, 233]
salary.each { |s| puts s }

# puts s = block body
# |s| = block arugments

# multiline block
salary.each do |s|
    a = 10
    res = a * s
    puts res
end

# block body
# a = 10
# res = a * s
# puts res

# block arugments
# |s|

Methods can take blocks implicitly and explicitly. If you want to call a block implicitly use the yield keyword. Yield finds the block and calls the passed block. Since you can pass implicit blocks, you don't have to call yield, and the block will be ignored.

# passing a block implicitly
def give_me_data
    puts "I am inside give_me_data method"
    yield
    puts "I am back in give_me_data method"
end

give_me_data { puts "Big data" }

# output
# I am inside give_me_data method
# Big data
# I am back in give_me_data method

# call multiple times
def give_me_data
    yield
    yield
    yield
end

give_me_data { puts "Big data" }

# output
# Big data
# Big data
# Big data

# call with block arguments

def give_me_data
    yield 10
    yield 100
    yield 30
end

give_me_data { |data| puts "Big data #{data} TB" }

# output
# Big data 10 TB
# Big data 100 TB
# Big data 30 TB

# call with multiple block arguments

def give_me_data
    yield "Big data", 10, "TB"
    yield "Big data", 100, "GB"
    yield "Big data", 30, "MB"
end

give_me_data { |text, data, unit| puts "#{text} #{data} #{unit}" }

# output
# Big data 10 TB
# Big data 100 GB
# Big data 30 MB

#  block will try to return from the current context
give_me_data
    puts "I am inside give_me_data method"
end

def test
    puts "I am inside test method"
    give_me_data { return 10 } # code returns from here
    puts "I am back in test method"
end

return_value = test

# output
# I am inside test method
# I am inside give_me_data method
# 10

# passing a block explicitly by using an ampersand parameter, here we are explicitly defining the method with block parameter and calling it
def give_me_data(&block)
    block.call
    block.call
end

give_me_data { puts "Big data" }

# output
# Big data
# Big data

How to check if a block is given

block parameter is mandatory when you call yield inside a method; otherwise, it will raise an exception

def give_me_data
    yield
end

give_me_data

# output
# LocalJumpError: no block given (yield)

# you can use block_given? method to handle the exception and make the block optional

def give_me_data
    return "no block" unless block_given?
    yield
end

give_me_data { puts "Big data" }
give_me_data

# output
# Big data

def give_me_data(&block)
    block.call if block
end

give_me_data { puts "Big data" }
give_me_data

# output
# Big data

Procs

A proc is like a block that can be stored in a variable.

p = Proc.new { puts "Hello World" }

def give_me_data(proc)
    proc.call
end

give_me_data p

# output
# Hello World

# arbitrary arguments
p = Proc.new { |count| "Hello World " * count }

def give_me_data(proc)
    proc.call 5, 2
end

give_me_data p

# output
# "Hello World Hello World Hello World Hello World Hello World "

#  proc will try to return from the current context
p = Proc.new { return 10 }
p.call

# output
LocalJumpError: unexpected return

# because you can’t return from the top-level context

def give_me_data
    puts "I am inside give_me_data method"
    p = Proc.new { return 10 }
    p.call # code returns from here
    puts "I am back in give_me_data method"
end

return_value = give_me_data
puts return_value

# output
# I am inside give_me_data method
# 10

Lambdas

Lambda is an anonymous function, wrap the lambda with do and end (for multiline) or curly brackets { and } (for a single line). Lambda returns the last evaluated statement.

# there are multiple ways to declare a lambda
l = lambda { puts "Hello World" }
# shorthand
l = -> { puts "Hello World" }

# call the lambda
l.call

# output
# Hello World

# there are multiple ways you can call a lambda
l.()
l[]

# strict arguments
l = -> (count) { "Hello World " * count }
l.call 5

# output
# "Hello World Hello World Hello World Hello World Hello World "

l.call 5, 2

# output
wrong number of arguments (given 2, expected 1)

# lambdas return from the lambda itself, like a regular method
l = -> { return 10 }
l.call

# output
# 10

def give_me_data
    puts "I am inside give_me_data method"
    l = -> { return 10 }
    l.call
    puts "I am back in give_me_data method"
end

return_value = give_me_data
puts return_value

# output
# I am inside give_me_data method
# I am back in give_me_data method
# nil # because puts return nil

Blocks VS Procs VS Lambdas

All of them are used for executing a single line or multiline code.

Array

Unlike other programming languages like Java, Ruby only has dynamic arrays but no static arrays. That means you don’t have to worry about the size of the array while adding new values.

There are multiple ways we can Initialize an empty array.

array = Array.new
# or
array = []

Fill an array with the initial size and a default object.

numbers = Array.new(3, 7)
# [7, 7, 7]
# or
numbers = [7, 7, 7]
# [7, 7, 7]
# or
numbers = []
numbers.fill(7, 0..2)
# [7, 7, 7]

How about an array with different hashes? No problem, Ruby has you covered!

array_with_hashes = Array.new(2) { {} }
# [{}, {}]
array_with_hashes[0][:name] = "Bob"
array_with_hashes[0][:id] = 10
# [{:name=>"Bob", :id=>10}, {}]

Let’s talk about 2D arrays briefly.

temperature_data = [
                     ["A908", 38],
                     ["A909", 37],
                     ["A910", 38],
                   ]
temperature_data[0]
# ["A908", 38]
temperature_data[0][0]
# "A908"
temperature_data[0][1]
# 38

Array indexing starts at 0. A negative index is relative to the end of the array, so -1 is the last element of the array, -2 is the second last element in the array, and so on.

numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
puts numbers[0]
# 1
puts numbers[-1]
# 10

# numbers.at
puts numbers.at(0)
# 1

Add values at the end of the array.

numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
numbers.push(11)
# [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11]
numbers.push(12, 13, 14)
# [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14]

Add values at the start of the array.

numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
numbers.unshift(0)
# [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
numbers.unshift(-3, -2, -1)
# [-3, -2, -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

Insert values at the given index.

numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
numbers.insert(0, 0)
# [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
numbers.insert(0, -3, -2, -1)
# [-3, -2, -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

numbers.insert(-1, 12, 13, 14)
# [-3, -2, -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 13, 14]
numbers.insert(-4, 11)
# [-3, -2, -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14]

How about a block to populate the values of an array?

numbers = Array.new(10) { |n| n = n * 2 }
# [0, 2, 4, 6, 8, 10, 12, 14, 16, 18]

It gets easier to fill an array.

numbers = Array(100..110)
# [100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110]
# or we can convert a range to an array
(100..110).to_a
# [100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110]

How to iterate an Array

There are multiple ways you can iterate an Array.

each

# when you have single line block
salary = [399, 234, 566, 533, 233]
salary.each { |s| puts s }
# output
# 399
# 234
# 566
# 533
# 233

# when you have a multiline block, you can replace the curly brackets {} with do and end
salary.each do |s|
  a = 10
  res = a * s
  puts res
end
# output
# 3990
# 2340
# 5660
# 5330
# 2330

# or you can do the same thing just using curly brackets {} and semicolons as separators instead of new lines
salary.each { |s| a = 10 ; res = a * s ; puts res }

each_with_index

salary = [399, 234, 566, 533, 233]
salary.each_with_index { |value, index| puts "#{index} #{value}" }
# output
# 0 399
# 1 234
# 2 566
# 3 533
# 4 233

each_with_object

colors = [{color: "red", count: 3}, {color: "red", count: 5}, {color: "black", count: 4}]
colors.each_with_object(Hash.new(0)) { |color, hash| hash["color_"+color[:color]] = color[:color].upcase; hash["count_"+color[:color]] += color[:count] }
# output
{"color_red"=>"RED", "count_red"=>8, "color_black"=>"BLACK", "count_black"=>4}

[1, 2, 3].each_with_object(0) { |number, sum| sum += number}
# output
# 0
# beacuse 0 is immutable, since the initial object is 0, the method returns 0

each_index

salary = [399, 234, 566, 533, 233]
salary.each_index { |i| puts i}
# output
# 0
# 1
# 2
# 3
# 4

map

salary = [399, 234, 566, 533, 233]
salary.map { |s|  s * 10  }
# returns
# [3990, 2340, 5660, 5330, 2330]

# on the other hand each returns the originl values
salary = [399, 234, 566, 533, 233]
salary.each { |s|  s * 10  }
# returns
# [399, 234, 566, 533, 233]

collect

salary = [399, 234, 566, 533, 233]
salary.collect { |s| s > 400 }
# output
# [false, false, true, true, false]

while

planets = ["Mercury", "Venus", "Earth", "Mars", "Jupiter", "Saturn", "Uranus", "Neptune"]
index = 0
while index < planets.size
    puts "#{planets[index]}"
    index += 1
end

a = 1
star = '*'
while a <= 10
    puts star
    star += '*'
    a += 1
end

do while

planets = ["Mercury", "Venus", "Earth", "Mars", "Jupiter", "Saturn", "Uranus", "Neptune"]
index = 0
loop do
    puts "#{planets[index]}"
    index += 1
    break if planets[index] == "Mars" or index > planets.size
end

for

for value in [2, 3, 5, 7]
    puts value
end

until

planets = ["Mercury", "Venus", "Earth", "Mars", "Jupiter", "Saturn", "Uranus", "Neptune"]
index = planets.size - 1
until index < 0
    puts "#{planets[index]}"
    index -= 1
end

a = 1
star = '*'
until star.length > 10
    puts star
    star += '*'
    a += 1
end

times

10.times { puts "#{rand(1..100)}"}
# output
# will print 10 random numbers

# just because you can doesn't mean you should iterate an array like this
data_sample = [2, 3, 5, 7]
data_sample.size.times { |index| puts "#{data_sample[index]}" }
# output
# 2
# 3
# 5
# 7

upto

data_sample = [2, 3, 5, 7]
0.upto((data_sample.size - 1) / 2) { |index| puts "#{data_sample[index]}" }
# output
# 2
# 3

downto

data_sample = [2, 3, 5, 7]
(data_sample.size - 1).downto(data_sample.size / 2) { |index| puts "#{data_sample[index]}" }
# output
# 7
# 5

step

1.step(20, 2) { |number| puts "#{number}"}
# output
# 1
# 3
# 5
# 7
# 9
# 11
# 13
# 15
# 17
# 19

19.step(1, -2) { |number| puts "#{number}"}
# output
# 19
# 17
# 15
# 13
# 11
# 9
# 7
# 5
# 3
# 1

inject

numbers = [2, 2, 2, 2, 2]
numbers.inject{ |res, n| res + n }
# output is the result of the sum of all numbers
# if you do not set an initial value for res, then the first element of the array is used as the initial value of res
# 10

# now set the value of res with 11
numbers = [2, 2, 2, 2, 2]
numbers.inject(11) { |res, n| res + n }
# so 11 + 2, 13 + 2, 15 + 2, 17 + 2 and 19 + 2
# 21

# using symbol
numbers = [2, 2, 2, 2, 2]
numbers.inject(:+)
# output
# 10

# using initial value and a symbol
numbers = [2, 2, 2, 2, 2]
numbers.inject(11, :+)
# output
# 21

reduce

numbers = [2, 2, 2, 2, 2]
numbers.reduce(11, :+)
# output
# 21

detect

planets = ["Mercury", "Venus", "Earth", "Mars", "Jupiter", "Saturn", "Uranus", "Neptune"]
planets.detect { |name| name.start_with?("E") and name.end_with?("h") }
# output
# Earth

salary = [399, 234, 566, 533, 233]
salary.detect { |s| s > 1000 }
# output
# nil

find

planets = ["Mercury", "Venus", "Earth", "Mars", "Jupiter", "Saturn", "Uranus", "Neptune"]
planets.find { |name| name.start_with?("E") and name.end_with?("h") }
# output
# Earth

select

numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
numbers.select { |n| n % 2 == 0 }
# now you have an array of even numbers, how cool is that
# [2, 4, 6, 8, 10]
# returns an empty array if there is no value that satisfy your logic
[1, 1, 1].select { |n| n % 2 == 0 }
# no even numbers
# []

reject

numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
numbers.reject { |n| n % 2 == 0 }
# reject if the number is even, so now we have an array of odd numbers
# [1, 3, 5, 7, 9]

keep_if

numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
numbers.keep_if { |n| n % 2 == 0 }
# numbers array holds only even numbers
# [2, 4, 6, 8, 10]

delete_if

numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
numbers.delete_if { |n| n % 2 == 0 }
# numbers array holds only odd numbers
# [1, 3, 5, 7, 9]

drop_while

numbers = [1, 2, 3, 1, 2, 3, 0]
numbers.drop_while { |n| n < 3 }
# is 3 less than 3, returns false, so drop 1, 2
# [3, 1, 2, 3, 0]

Boolean Enumerable methods

all?

[2, 4, 6, 8, 10].all? { |num| num % 2 == 0 }
# true
[1, 4, 6, 8, 10].all? { |num| num % 2 == 0 }
# false

any?

[1, 3, 5, 7, 10].any? { |num| num % 2 == 0 }
# true
[1, 3, 5, 7, 19].any? { |num| num % 2 == 0 }
# false

one?

[1, 3, 2, 5, 7].one? { |num| num % 2 == 0 }
# true
[1, 3, 2, 5, 4].one? { |num| num % 2 == 0 }
# false

none?

[1, 3, 5, 7, 9].none? { |num| num % 2 == 0 }
# true
[2, 3, 5, 7, 9].none? { |num| num % 2 == 0 }
# false

empty?

[].empty?
# true
[1, 3, 5, 7, 9].empty?
# false

How to check if a value exists in an Array (include?)

planets = ["Mercury", "Venus", "Earth", "Mars", "Jupiter", "Saturn", "Uranus", "Neptune"]
planets.include? "Mars"
# output
# true

planets.include? "Pluto"
# output
# false

How to get array size

# you can either use size or length, both are synonymous
planets = ["Mercury", "Venus", "Earth", "Mars", "Jupiter", "Saturn", "Uranus", "Neptune"]
planets.size
# output
# 8

planets.length
# output
# 8

How to clear an Array

numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
numbers.clear
# output
# []

How to get the first element of an Array

numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
numbers[0]
# or
numbers.first
# output
# 1

How to get the last element of an Array

numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
numbers[-1]
# or
numbers.last
# output
# 10

How to merge two Arrays

a = ["tom", "mot", "otm"]
b = [2, 3, 5]

a.zip(b)

# outout
# [["tom", 2], ["mot", 3], ["otm", 5]]

How to sort an Array

primes = [7, 2, 3, 5]
sorted_primes = primes.sort
puts "#{sorted_primes}"
# output
# [2, 3, 5, 7]

or in-place sort

primes = [7, 2, 3, 5]
primes.sort!
puts "#{primes}"
# output
# [2, 3, 5, 7]

planets = ["Mercury", "Venus", "Earth", "Mars", "Jupiter", "Saturn", "Uranus", "Neptune"]
planets.sort
# output
# ["Earth", "Jupiter", "Mars", "Mercury", "Neptune", "Saturn", "Uranus", "Venus"]

planets.sort_by { |p| p }
# output
# ["Earth", "Jupiter", "Mars", "Mercury", "Neptune", "Saturn", "Uranus", "Venus"]

planets.sort_by { |p| p.length }
# output
# ["Mars", "Earth", "Venus", "Saturn", "Uranus", "Neptune", "Jupiter", "Mercury"]

How to get the maximum from an Array

primes = [7, 2, 3, 5]
primes.max_by { |p| p }
# output
# 7

How to get Array elements using a range

# numbers[start..end], both index are inclusive
puts numbers[0..3]
# 1
# 2
# 3
# 4

# numbers[start..end], end index is exclusive
puts numbers[0...3]
# 1
# 2
# 3

# or numbers[start..length]
puts numbers[0, 1]
# 1

How to get first n elements of an Array

primes = [7, 2, 3, 5]
primes.take(3)
# [7, 2, 3]

How to access an element

primes = [7, 2, 3, 5]
primes.fetch(3)
# 5
# Fetch will throw an error if the element does not exist
primes.fetch(10)
# (index 10 outside of array bounds: -4...4)
# or get an default value
primes.fetch(10, -1)
# -1

How to remove one or more elements of an Array

Remove first n elements.

primes = [7, 2, 3, 5]
primes.drop(3)
# [5]

Remove first element.

primes = [7, 2, 3, 5]
primes.shift
# [2, 3, 5]

Remove last element.

primes = [7, 2, 3, 5]
primes.pop
# [7, 2, 3]

Remove element with an Index.

primes = [7, 2, 3, 5]
primes.delete_at(-1)
# [7, 2, 3]

Remove all occurrences of an element.

primes = [7, 2, 3, 5, 5]
primes.delete(5)
# [7, 2, 3]

How to remove duplicate elements from an Array

numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 10, 1]
numbers.uniq
# [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

Hash

Let's start with some basic operations. Below we have an example of how to initialize an empty hash.

students = Hash.new
or
students = {}

Here we have an empty hash, without any key-value pairs. Now the question is, what if someone wants to access a key that does not exist in the hash? Well, the answer is nil, which is the default value.

puts "#{students[:name]}"
# nil

Let’s add some values to the hash using symbols. There are two ways to declare symbols as keys.

students = Hash.new
students = {name: 'John', email: '[email protected]'}
puts "#{students[:name]}"
# or
students = Hash.new
students = {:name => 'John', :email => '[email protected]'}
puts "#{students[:name]}"

I prefer the former one because I’ve to type less! How about initializing with default values, here we have initialized an empty hash with a default value of “no email” for every key.

students = Hash.new("no data")
puts "#{students[:email]}"
# no email
# or
students = Hash.new
students.default = "no data"
puts "#{students[:email]}"
# no email

The Hash.new() creates a single default object for every key. That’s why by altering it for one key changes for other keys as well. For example, when we change the default value for the key id, it affects other unassigned key’s default value, in this case, name.

students = Hash.new("no data")
students[:email] = "[email protected]"
puts "#{students[:email]}"
# [email protected]
puts "#{students[:id]}"
# no data
puts "#{students[:name]}"
# no data
students[:id].upcase!
puts "#{students[:email]}"
# [email protected]
puts "#{students[:id]}"
# NO DATA
puts "#{students[:name]}"
# NO DATA

If the above code behavior is not desired, you can use Hash.new {|hash, key| block } instead. This method creates a default object each time for different keys.

students = Hash.new {|hash, key| hash[key] = "no data" }
students[:email] = "[email protected]"
puts "#{students[:email]}"
# [email protected]
puts "#{students[:id]}"
# no data
puts "#{students[:name]}"
# no data
students[:id].upcase!
puts "#{students[:email]}"
# [email protected]
puts "#{students[:id]}"
# NO DATA
puts "#{students[:name]}"
# no data

In short, Hash.new(some_value) sets a default value of some_value for every key that does not exist in the hash, Hash.new {|hash, key| block } creates a new default object for every key that does not exist in the hash, and Hash.new() or {} sets nil for every key.

How to group by count

numbers = [1, 1, 1, 2, 4, 65, 55, 54, 55]
freq_hash = numbers.each_with_object(Hash.new(0)) { |number, hash| hash[number] += 1 }
puts "#{freq_hash}"
# output
# {1=>3, 2=>1, 4=>1, 65=>1, 55=>2, 54=>1}

or

numbers = [1, 1, 1, 2, 4, 65, 55, 54, 55]
freq_hash = Hash.new(0)
numbers.each { |number| freq_hash[number] += 1 }
puts "#{freq_hash}"
# output
# {1=>3, 2=>1, 4=>1, 65=>1, 55=>2, 54=>1}

or from Ruby 2.7+

numbers = [1, 1, 1, 2, 4, 65, 55, 54, 55]
numbers.tally
# output
# {1=>3, 2=>1, 4=>1, 65=>1, 55=>2, 54=>1}

What's the difference between Hash.new(0) and {}

# Hash.new(0) sets a default value of 0 for every key that do not exist in the hash.
# {} or Hash.new() sets nil for every key

h1 = Hash.new(0)
h1[:count] += 1
puts "#{h1[:count]}"
# output
# 1

puts "#{h1[:new_key]}"
# output
# 0

h2 = {}
h2[:count] += 1
# error
undefined method `+' for nil:NilClass

How to sort a Hash

hash = {e: 2, d: 3, c: 5, b: 7, a: 11}
hash.sort
# output
# [[:a, 11], [:b, 7], [:c, 5], [:d, 3], [:e, 2]]

hash.sort_by { |k, v| k }
# output
# [[:a, 11], [:b, 7], [:c, 5], [:d, 3], [:e, 2]]

hash.sort_by { |k, v| v }
# output
# [[:e, 2], [:d, 3], [:c, 5], [:b, 7], [:a, 11]]

How to get the maximum from a Hash

hash = {e: 2, d: 3, c: 5, b: 7, a: 11}
hash.max_by { |k, v| v }
# output
# [:a, 11]

Loop

How to break out from loop

# by using break keyword
salary = [399, 234, 566, 533, 233]
salary.each do |s|
    break if s == 566
    puts s
end
#output
# 399
# 234

How to skip inside a loop

# by using next keyword
salary = [399, 234, 566, 533, 233]
salary.each do |s|
    next if s == 533
    puts s
end
# output
# 399
# 234
# 566
# 233

How to repeat the current iteration

data = [456, 3000]
retry_count = 0
status = "network failure"
sum = 0
data.each do |d|
    if retry_count == 3
        status = "connection established"
        retry_count = 0
        redo
    elsif status == "network failure" and retry_count < 5
        puts "network failure #{retry_count}"
        retry_count += 1
        redo
    elsif status == "connection established"
        puts d
        sum += d
    end
end

# output of sum
# 3456

How to restart a loop

numbers = [2, 2, 44, 44]
sum = 0
begin
    numbers.each do |s|
        if rand(1..10) == 5
            puts "hi 5, let's do it again!"
            sum = 0
            raise "hi 5"
        end
        puts s
        sum += s
    end
rescue
    retry
end

Classes

class Person
    # when you create a new object, it looks for a method named initialize and executes it, like a constructor in java
    # def initialize(name, number)
    #    @name = name
    #    @number = number
    # end

    # instance variable
    # @name

    # class variable
    # @@count

    # attr_accessor acts as a getter and setter for the following instance attributes
    attr_accessor :name, :number

    # class variable must be initialized
    @@count = 0

    def self.count
        @@count
    end

    def self.count=(count)
        @@count = count
    end

    def initialize
        @@count += 1
    end
end

# create an instance of the Person class
p1 = Person.new

# set attributes of the Person class
p1.name = "Yukihiro Matsumoto"
p1.number = 9999999999

# get attributes of the Person class
puts "#{p1.name}"
puts "#{p1.number}"
puts "#{Person.count}"

# Yukihiro Matsumoto
# 9999999999
# 1

p2 = Person.new
p2.name = "Yukihiro Matsumoto"
p2.number = 9999999999

# get attributes of the Person class
puts "#{p2.name}"
puts "#{p2.number}"
puts "#{Person.count}"

# Yukihiro Matsumoto
# 9999999999
# 2

# set class variable
Person.count = 3
puts "#{Person.count}"
# 3

How to inherit a class

class Person
    attr_accessor :name, :number
end

# use < symbol to inherit methods and attributes from the parent class
class Student < Person
    attr_accessor :id
end

s = Student.new

s.name = "James Bond"
s.number = 700
s.id = 678

puts "#{p.name}"
James Bond

puts "#{p.number}"
700

puts "#{p.id}"
678

How to check instance type

# Returns true if the object is an instance of the given class, not a subclass or superclass
class Vehicle; end
class Car < Vehicle; end
class Audi < Car; end

car = Car.new
car.instance_of? Vehicle
false
car.instance_of? Car
true
car.instance_of? Audi
false

a = 7
a.instance_of? Integer
true
a.instance_of? Numeric
false

Print all method names of a class

puts (String.methods).sort
# Exclude methods that are inherited from Object class
puts (String.methods - Object.public_instance_methods).sort

Check if a Class has a particular method

String.respond_to?(:prepend)
true
String.respond_to?(:append)
false

Modules

Modules are used for combining similar methods, so that other classes or modules can use it. You can not instantiate a module (like abstract classes in Java)

module MyRandomHelper
    def roll_dice
      rand(1..6)
    end
end

class Person
    attr_accessor :name, :number
end

class Player < Person
    include MyRandomHelper
    attr_accessor :score
end

p = Player.new
p.roll_dice

TODO

Operator Overloading

class Vector
    attr_accessor :x, :y

     def initialize(x, y)
        @x = x
        @y = y
    end

    def +(second)
        Vector.new(@x + second.x, @y + second.y)
    end

    def -(second)
        Vector.new(@x - second.x, @y - second.y)
    end

    def *(second)
        Vector.new(@x * second.x, @y * second.y)
    end

    def /(second)
        Vector.new(@x / second.x, @y / second.y)
    end

    def to_s
        return "(#{@x}, #{@y})"
    end

end

v1 = Vector.new(5, 10)
v2 = Vector.new(4, 9)

puts v1 + v2
puts v1 - v2
puts v1 * v2
puts v1 / v2

Exception Handling

begin
    puts 'before the raise'
    raise 'raise an exception'
    puts 'after the raise'
rescue
    puts 'rescued'
end

begin
    raise StandardError, 'standard error occurred'
rescue StandardError => e
    puts "#{e.class}: #{e.message}"
    puts e.backtrace.inspect
end

$! contains the raised exception $@ contains the exception backtrace

begin
    raise StandardError, 'standard error occurred'
rescue StandardError
    puts "#{$!.class}: #{$!.message}"
    puts "#{$@}"
end

retry re-executes the code inside begin end block

retry_count = 1

begin
    puts "retry count: #{retry_count}"
    retry_count += 1
    raise 'raise an exception'
rescue
    retry if retry_count <= 5
end

Custom exception

class MyException < Exception
end

begin
    raise MyException, 'my exception occurred'
rescue MyException
    puts "#{$!.class}: #{$!.message}"
    puts "#{$@}"
end

Catch multiple exceptions

begin
    raise 'i am a string'.call
rescue NoMethodError => e
    puts "#{$!.class}: #{$!.message}"
rescue ZeroDivisionError => e
    puts "#{$!.class}: #{$!.message}"
end

Further readings

Regular expression

a = "Better a diamond with a flaw than a pebble without"
a[/(\w+)/]

# output
# "Better"

a[/(\w+) (\w+)/]

# output
# "Better a"

a[/(?<one>\w+) (?<two>\w+)/, :two]
# output
# "a"

Miscellaneous

How to generate random number

rand(max=0)

# when calling it without an argument, rand returns a floating point number between 0.0 (including) and 1.0 (excluding), under the hood max.to_i.abs == 0
rand

# output
# 0.055758056734957595

# when the argument value is greater than or equal to 1, rand returns a integer between 0 (including) and that number (excluding), under the hood max.to_i.abs >= 1
rand(100)

# output
# 7

# generating number between 2 numbers both inclusive
rand(150..170)

# output
# 167

# generating number between 2 numbers, the last number is not inclusive
rand(1...10)

# output
# 4

Check the syntax of a Ruby file

ruby -c filename.rb

Concatenate String in a loop

words = ["Lorem", "ipsum", "dolor", "sit", "amet"]
words.map { |word| word.downcase }.join(' ')

# output
# "lorem ipsum dolor sit amet"

CamelCase String split

sentence = "ThereIsNoSpoon"
words = sentence.split(/(?=[A-Z])/)

# output
# ["There", "Is", "No", "Spoon"]

Ruby scripts

Platforms that supports Ruby

1. Heroku
2. Vercel
3. AWS Lambda
4. Fly.io

Ruby frameworks

1. Ruby on Rails
2. Sinatra
3. Padrino

My Ruby Articles

1. A Beginner’s Guide To Ruby
2. 17 Useful Ruby String Methods to Clean and Format Your Data
3. How to Deploy a Ruby Serverless Function to Vercel
4. Useful Ruby Array Methods to Manage Your Data
5. An Introduction to Ruby Hashes
6. How to Dockerize an Existing Sinatra Application
7. How To Dockerize an Existing Ruby on Rails Application
8. How To Parse Data Using Ruby and Selenium

Books and other resources

1. Ruby doc
2. How to use Ruby’s English and/or operators without going nuts
3. What is attr_accessor in Ruby?
4. Ruby Module Mixin Awesomeness
5. Tutorials
6. Pattern matching - New feature in Ruby 2.7
7. Awesome Ruby Blogs
8. Ruby Scripts
9. Awesome Ruby
10. Ruby Bookmarks
11. Code With Jason

Bug Reports and Feature Requests

Please create an issue with as much information you can. Thank you.

Contribution Guidelines

Author

Mahbub Zaman (https://mahbub.ninja)

License

MIT License