date_format does not work correctly on hms objects #88

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1. karawoo commented on Jun 14, 2017

   

   karawoo

   on Jun 14, 2017

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   If I understand correctly the issue here is that date_format behaves differently for POSIXct and hms objects, and for hms objects it shows seconds even when the format requested is only "%H:%M". A more illustrative example is below:

   library(hms)
   library(scales)
   
   t <- Sys.time()
   
   date_format("%H:%M", tz = "GMT")(t)
   #> [1] "17:22"
   date_format("%H:%M", tz = "GMT")(as.hms(t))
   #> [1] "17:22:08.155499"
   
   format(t, "%H:%M", tz = "GMT")
   #> [1] "17:22"
   format(as.hms(t), "%H:%M", tz = "GMT")
   #> [1] "17:22:08.155499"

   date_format uses format under the hood, so that is why they behave the same. @hadley do you think this behavior should change? Or is this issue more appropriate for the hms package?
2. hadley commented on Jun 14, 2017

   

   hadley

   on Jun 14, 2017

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   We should probably add support for hms.
3. karawoo

   added

   featurea feature request or enhancementa feature request or enhancement

   on Jun 14, 2017
4. hadley

   assigned

   dpseidel

   on Jun 5, 2018
5. dpseidel commented on Jun 7, 2018

   

   dpseidel

   on Jun 7, 2018

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   So this is caused because the format.hms method converts hms objects to character, ultimately calling format.Default and ignoring the format argument to date_format (and the underlying methods format.POSIXlt and format.POSIXct)

   Assuming we want to fix this in scales without adjusting the format.hms method itself, the simplest way is to call format.Date directly, although I think this is generally considered bad practice. format.Date and strftime (just a wrapper for format.POSIXlt) seem to differ in how the timezone is treated but (with proper consideration of the timezone) either will output the expected result (as shown using strftime in the OP).

   This fix of course stops making sense when a user provides an hms object and asks for a format containing dates not just hours minutes and seconds (as is currently the default for date_format). Perhaps it's worth providing hms support in a separate function time_format? Or is it more desirable to generalize date_format with specific handling of hms objects so they print using a format method for date/time objects?
6. hadley commented on Jun 14, 2018

   

   hadley

   on Jun 14, 2018

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   I'd rewrite date_format() along these lines:

   date_format <- function(format = "%Y-%m-%d", tz = 'UTC') {
     function(x) {
       if (inherits(x, "POSIXt")) {
         format(x, format, tz = tz)  
       } else if (inherits(x, "Date")) {
         
       } else if (inherits(x, "difftime")) {
         
       } else {
         stop("Unsupported type (needs better error message)")
       }
         
     }
   }

   Alternatively, it might be better to add a custom time format type — it's a bit odd to use date_format() with a time.
7. dpseidel

   added 3 commits that reference this issue on Jun 27, 2018

   Add time_format() function for time formatting

   ...

   This issue will close once commit eca802e is merged into the 'master' branch.

   eca802e

   Add time_format() function for time formatting

   ...

   This issue will close once commit ea9ab61 is merged into the 'master' branch.

   ea9ab61

   Add time_format() function for time formatting

   ...

   This issue will close once commit 9d04747 is merged into the 'master' branch.

   9d04747
8. dpseidel

   closed this as completedin ad6f084on Jun 28, 2018