[R] how to change format of dates in a tibble

[Duncan Murdoch]

On 18/12/2019 11:45 a.m., Christopher W Ryan wrote:
> I'm not understanding how the tidyverse handles date formats.
> 
> output of sessionInfo() at the end of my message.
> 
> dateRanges <- structure(list(apptType = structure(1:2, .Label = c("initial
> visit",
> "start of treatment visit"), class = "factor"), minMadeRequestDates =
> structure(c(18124,
> 18115), class = "Date"), maxMadeRequestDates = structure(c(18187,
> 18199), class = "Date"), minApptDate = structure(c(18129, 18129
> ), class = "Date"), maxApptDate = structure(c(18199, 18214), class =
> "Date")), class = c("tbl_df",
> "tbl", "data.frame"), row.names = c(NA, -2L))
> str(dateRanges)
> 
> ## produces desired result
> format(dateRanges, format = "%d %b %Y")
> 
> ## does not produce desired result
> library(dplyr)
> format(dateRanges, format = "%d %b %Y")
> 
> ## rather cumbersome, and also does not produce the desired output
> mutate(dateRanges, minMRD = as.Date(minMadeRequestDates, format = "%d %b
> %Y"))
> 
> How does one change the format of a date variable inside a tibble when
> dplyr is loaded?
In the first example, the class of dateRanges is c("tbl_df", "tbl", 
"data.frame").   Since you don't have any tbl methods loaded, you get 
the format.data.frame method.

When you attach dplyr, it loads the tibble package, and it has a 
"format.tbl" method that gives the output you don't like.

One simple way to work around this is to call the format.data.frame 
method directly:

  format.data.frame(dateRanges, format = "%d %b %Y")

Similarly,

  format(as.data.frame(dateRanges), format = "%d %b %Y")

calls that method.

You can also convert the date columns to char using something like

   dateRanges %>% mutate_all(function(x) format(x, format = "%d %b %Y"))

and then auto-printing will show you the formatted output.  This is a 
little risky, since it applies the formatting function to all columns; 
in your example it works, but you might need to use mutate_if() instead:

   dateRanges %>% mutate_if(~ inherits(.x, "Date"), ~ format(.x, "%d %b 
%Y"))

Duncan Murdoch

> 
> Thanks
> 
> Chris Ryan
> 
> ======== session info ===========
>> sessionInfo()
> R version 3.6.1 (2019-07-05)
> Platform: i386-w64-mingw32/i386 (32-bit)
> Running under: Windows 7 (build 7601) Service Pack 1
> 
> Matrix products: default
> 
> locale:
> [1] LC_COLLATE=English_United States.1252  LC_CTYPE=English_United
> States.1252    LC_MONETARY=English_United States.1252
> [4] LC_NUMERIC=C                           LC_TIME=English_United
> States.1252
> 
> attached base packages:
> [1] stats     graphics  grDevices utils     datasets  methods   base
> 
> other attached packages:
> [1] dplyr_0.8.3
> 
> loaded via a namespace (and not attached):
>   [1] Rcpp_1.0.2       fansi_0.4.0      zeallot_0.1.0    utf8_1.1.4
> crayon_1.3.4     assertthat_0.2.1 R6_2.4.0
>   [8] backports_1.1.5  magrittr_1.5     pillar_1.4.2     rlang_0.4.0
>   cli_1.1.0        vctrs_0.2.0      glue_1.3.1
> [15] purrr_0.3.3      compiler_3.6.1   pkgconfig_2.0.3  tidyselect_0.2.5
> tibble_2.1.3
> ====================================
> 
> 	[[alternative HTML version deleted]]
> 
> ______________________________________________
> R-help using r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>