write_csv() returns modified tibble instead of input

[adamroyjones]

The subject describes the issue fully. Below is a working example. Versions are:

• R 3.5.2 (on Ubuntu 16.04.5 LTS on x86_64),
• readr 1.3.1,
• magrittr 1.5,
• lubridate 1.7.4, and
• tibble 2.0.1.

library(tibble)
library(lubridate)
library(magrittr)
library(readr)

tbl = tribble(
  ~date, ~value,
  ymd("2019-05-05"), 1
)

tbl # class(tbl$date[1]) = "Date"

tbl = tbl %>% write_csv("tmp.csv")

tbl # class(tbl$date[1]) = "character"

[cderv]

This comes from here

readr/R/write.R

Lines 62 to 71 in 271bb3f

	write_delim <- function(x, path, delim = " ", na = "NA", append = FALSE,
	col_names = !append, quote_escape = "double") {
	stopifnot(is.data.frame(x))
	x[] <- lapply(x, output_column)
	stream_delim(x, path, delim = delim, col_names = col_names, append = append,
	na = na, quote_escape = quote_escape)
	invisible(x)
	}

line 66: x is modified to be prepared for writing as text ouput in a text file. And the function will return this modified object instead of the original one. Converting date (and other types) to character is one of the change.

However, the documentation says

write_*() returns the input x invisibly.

So, this seems like a bug or a documentation with not enough precision 🤔

[gadenbuie]

This was not the behavior of write_csv() in earlier versions of readr. I'm not sure of the version where this bug was introduced, but I tested on version 1.1.1 before upgrading to version 1.3.1, and the input was returned intact.

Here's a more complete reprex showing that this also applies to factors that are converted to characters for writing to csv.

library(tidyverse)
library(lubridate)

x <- tibble(
  x = factor(letters[1:4]),
  y = now(tz = "America/New_York") - days(0:3)
)

y <- write_csv(x, "tmp.csv")

identical(x, y)
#> [1] FALSE

x
#> # A tibble: 4 x 2
#>   x     y                  
#>   <fct> <dttm>             
#> 1 a     2019-03-21 21:56:29
#> 2 b     2019-03-20 21:56:29
#> 3 c     2019-03-19 21:56:29
#> 4 d     2019-03-18 21:56:29
y
#> # A tibble: 4 x 2
#>   x     y                   
#>   <chr> <chr>               
#> 1 a     2019-03-22T01:56:29Z
#> 2 b     2019-03-21T01:56:29Z
#> 3 c     2019-03-20T01:56:29Z
#> 4 d     2019-03-19T01:56:29Z
read_csv("tmp.csv")
#> # A tibble: 4 x 2
#>   x     y                  
#>   <chr> <dttm>             
#> 1 a     2019-03-22 01:56:29
#> 2 b     2019-03-21 01:56:29
#> 3 c     2019-03-20 01:56:29
#> 4 d     2019-03-19 01:56:29

^{Created on 2019-03-22 by the reprex package (v0.2.1)}

Session info

devtools::session_info()
#> ─ Session info ──────────────────────────────────────────────────────────
#>  setting  value                       
#>  version  R version 3.5.1 (2018-07-02)
#>  os       Ubuntu 18.04.1 LTS          
#>  system   x86_64, linux-gnu           
#>  ui       X11                         
#>  language (EN)                        
#>  collate  C.UTF-8                     
#>  ctype    C.UTF-8                     
#>  tz       Etc/UTC                     
#>  date     2019-03-22                  
#> 
#> ─ Packages ──────────────────────────────────────────────────────────────
#>  package     * version    date       lib source                        
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[gadenbuie]

May I suggest renaming this issue to "write_csv() returns modified tibble instead of input" (or something similar)?

Also, write_delim() previously distinguished between the input and modified output tables.

readr/R/write.R

Lines 62 to 71 in ddbb5f4

	write_delim <- function(x, path, delim = " ", na = "NA", append = FALSE,
	col_names = !append) {
	stopifnot(is.data.frame(x))
	x_out <- lapply(x, output_column)
	stream_delim(x_out, path, delim, col_names = col_names, append = append,
	na = na)
	invisible(x)
	}

[cderv]

For reference, the change were x_out was removed happened here ba7edb5 in a commit to fix a bug regarding datetime conversion

[adamroyjones]

@gadenbuie: You're quite right—it's a better subject. I've made the change.

[lock]

This old issue has been automatically locked. If you believe you have found a related problem, please file a new issue (with reprex) and link to this issue. https://reprex.tidyverse.org/