DataFrame#plot should provide more informative error message.

[matugm]

As mentioned in #478 I find that some error messages could be improved to provide a better user experience.

For example:

require 'daru'

df = Daru::DataFrame.new(
  { "Row 1" => [1, 2, 3],
    "Row 2"  =>  [3, 4, 5]
  }
)

df.plot(type: :bar, x: "Row 1")

Results in:

NoMethodError (undefined method `to_sym' for nil:NilClass)

But this error doesn't help the user understand that there is a missing y value.

There are other errors like these where missing or incorrect data leads into an exception.

Another Example:

If you don't provide a plot type at all you get "NameError (wrong constant name)". It may be more helpful to provide a list of valid plot types in this case.

[Shekharrajak]

Yes! There should be begin, rescue block to handle any kind of error coming from another gem. It must throw an error with the correct input type.

[Shekharrajak]

We can have a custom error class for daru library.