Add column specification as in readr

[dpprdan]

It would be nice to have the same column guessing with the same syntax as in readr. https://github.com/hadley/readr/releases/tag/v1.0.0

[jennybc]

A specific request that appears in #81, at the very least, is to make it easy to set one column type for all columns. Done in readr via, e.g., cols(.default = "c").

Updated: now implemented within the existing readxl style, i.e. if col_types has length one it is recycled for all columns.

[jennybc]

It would be nice to specify col type for certain columns and allow others to be guessed.

Update: now implemented within the existing readxl style.

[jennybc]

It would be nice to know whether a col type was guessed or specified by user. Conceivably we would warn less (and maybe even coerce more aggressively?) if the type was requested vs. guessed.

[jennybc]

I've edited the title to reflect my current thinking: it would be good to align with readr re: explicit column specification (including skipping and guessing, which is already supported). But I don't ever see doing readr-style column guessing. readr guesses based on data, which it must. readxl guesses based on Excel types, which -- I argue -- it must.

[nickbond]

Setting aside the guessing of formats, it would be good to at least align the syntax with readr. At the moment read_excel uses col_types "text" for example, whereas readr functions refer to "character".

[llrs]

I asked in #571 to be able to supply a long list of named col_type and use it when the name of the column matches a name on the col_type argument. If I understood correctly readr col_type argument if a column name is not present it doesn't try to guess the type of the column.

library("readr")
mtcars_csv <- system.file("extdata", "mtcars.csv", package="readr")
col_types_list <- cols_only(
    mpg = col_double(),
    cyl = col_integer(),
    disp = col_double()
)
df1 <- read_csv(mtcars_csv, col_types=col_types_list)
ncol(df1) == 3
df2 <- read_csv(mtcars_csv)
ncol(df2) == 11

I think that readxl should try to guess the column types if the type is not provided. Thanks!

[TreyRoady]

The ability to specify column types by name is absolutely key for large data sets with many columns.

In my case, I'm importing internal enterprise data reports. Read_excel is currently mangling the date-time objects in it, and the ability to go back and tweak just that column would be absolutely invaluable. Otherwise, I'm having to go back and hand-define hundreds of columns just to redefine one.

[jennybc]

This is on the roadmap for my next several months. The plan is to do a major upgrade of the col spec here at the same time as adding similar functionality to googlesheets4.

[dpprdan]

@llrs

If I understood correctly readr col_type argument if a column name is not present it doesn't try to guess the type of the column.

This depends on whether you specify the column types list (or col_spec) with cols_only() or cols().

1. If you specify it with cols_only(), like you did in your example, columns that are not present in your specification are skipped (cols_only() implicitly sets .default = col_skip()).
2. If you specify the col_spec with cols(), columns that are not present in your specification are guessed (cols() implicitly sets .default = col_guess()).

See also https://readr.tidyverse.org/reference/cols.html

[llrs]

Thanks for the clarification @dpprdan

[kristjan-kure]

Any updates?

[jennybc]

https://github.com/tidyverse/tidyverse.org/pull/569

What's coming next? I won't go so far as to promise that 2022 is the year of readxl 😉. But I can say that top priorities include equipping readxl with better problem reporting and column specification, making its interface feel more similar to that of readr and vroom.

[jxu]

As of version 1.4.2, the docs say col_types takes only a character vector. Is there a possibility to take a named list, guessing for the unspecified columns?

[diegomsg]

Until this is not implemented, a workaround I am adopting is using the functions below:

define_readxl_types <- function(col_nms, vec_names, vec_types, default_type = "guess") {
  #get names from earlier readxl without types
  cols <- dplyr::tibble(
    name = col_nms,
    index = seq(1:length(col_nms)),
    type = default_type
  )
  
  #build names and types
  col_def <- dplyr::tibble(
    name = vec_names,
    type = vec_types
  )
  
  #get indexes
  col_def$index <- purrr::map_vec(col_def$name, ~match(.x, cols$name))
  
  #iterate defined types
  for (i in 1:length(col_def)) {
    cols$type[col_def$index[i]] <- col_def$type[i]
  }
  
  #return types vector
  return(cols$type)
}

Probably this is not the best solution, best implementation. It works, though.

Example using readxl example:

> original <- read_excel(readxl_example("deaths.xlsx"), skip = 4)
> str(original)
tibble [14 × 6] (S3: tbl_df/tbl/data.frame)
 $ Name         : chr [1:14] "David Bowie" "Carrie Fisher" "Chuck Berry" "Bill Paxton" ...
 $ Profession   : chr [1:14] "musician" "actor" "musician" "actor" ...
 $ Age          : chr [1:14] "69" "60" "90" "61" ...
 $ Has kids     : chr [1:14] "TRUE" "TRUE" "TRUE" "TRUE" ...
 $ Date of birth: POSIXct[1:14], format: "1947-01-08" "1956-10-21" "1926-10-18" "1955-05-17" ...
 $ Date of death: chr [1:14] "42379" "42731" "42812" "42791" ...

> solution <- read_excel_with_some_types(
+   readxl_example("deaths.xlsx"), skip = 4,
+   vec_names =  c("Age", "Has kids"), vec_types = c("numeric", "logical") )
Warning messages:
1: Expecting numeric in C18 / R18C3: got 'at the' 
2: Expecting logical in D18 / R18C4: got 'bottom,' 
> str(solution)
tibble [14 × 6] (S3: tbl_df/tbl/data.frame)
 $ Name         : chr [1:14] "David Bowie" "Carrie Fisher" "Chuck Berry" "Bill Paxton" ...
 $ Profession   : chr [1:14] "musician" "actor" "musician" "actor" ...
 $ Age          : num [1:14] 69 60 90 61 57 69 82 89 99 53 ...
 $ Has kids     : logi [1:14] TRUE TRUE TRUE TRUE TRUE FALSE ...
 $ Date of birth: POSIXct[1:14], format: "1947-01-08" "1956-10-21" "1926-10-18" "1955-05-17" ...
 $ Date of death: chr [1:14] "42379" "42731" "42812" "42791" ...

Didn't tested it extensively, give it a try.

[jxu]

@diegomsg if you want the interface to be consistent with readr, the function should take a named list as col guesses

[asadow]

Echoing @nickbond, I agree on having the syntax match readr. I don't have opinions on which way, but given the same argument name col_types (and Jenny's affiliation), I expected allowable values for col_type to be the same.