Data.table: fcase doesn't recognize S4 object : lubridate example

[torema-ed]

Thank you all for the hard work in creating fcase. I have tried it out on a project that I'm currently working on and encountered problems when it was used together with lubridate period creation functions. It seems to recognize lubridate::weeks, lubridate::months, lubridate::years as lubridate::days.

reprex:

# Loading packages --------------------------------------------------------

library(data.table)
library(lubridate)
#> 
#> Attaching package: 'lubridate'
#> The following objects are masked from 'package:data.table':
#> 
#>     hour, isoweek, mday, minute, month, quarter, second, wday, week,
#>     yday, year
#> The following object is masked from 'package:base':
#> 
#>     date
library(lest)

# Creating test data ------------------------------------------------------

dt <- data.table(period_unit = c("days", "months", "weeks", "years"),
                 period_length = rep(1, times = 4))

# fcase output ------------------------------------------------------------

dt[, period := fcase(period_unit == "days", days(period_length),
                     period_unit == "months", months(period_length),
                     period_unit == "weeks", weeks(period_length),
                     period_unit == "years", years(period_length))][]
#>    period_unit period_length      period
#> 1:        days             1 1d 0H 0M 0S
#> 2:      months             1 1d 0H 0M 0S
#> 3:       weeks             1 1d 0H 0M 0S
#> 4:       years             1 1d 0H 0M 0S

# case_when output --------------------------------------------------------

dt[, period := case_when(period_unit == "days" ~ days(period_length),
                         period_unit == "months" ~ months(period_length),
                         period_unit == "weeks" ~ weeks(period_length),
                         period_unit == "years" ~ years(period_length))][]
#>    period_unit period_length            period
#> 1:        days             1       1d 0H 0M 0S
#> 2:      months             1    1m 0d 0H 0M 0S
#> 3:       weeks             1       7d 0H 0M 0S
#> 4:       years             1 1y 0m 0d 0H 0M 0S

^{Created on 2019-12-19 by the reprex package (v0.3.0)}

Session info

devtools::session_info()
#> ─ Session info ───────────────────────────────────────────────────────────────
#>  setting  value                       
#>  version  R version 3.6.2 (2019-12-12)
#>  os       Linux Mint 18.3             
#>  system   x86_64, linux-gnu           
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#>  language en_SG:en                    
#>  collate  en_SG.UTF-8                 
#>  ctype    en_SG.UTF-8                 
#>  tz       Asia/Singapore              
#>  date     2019-12-19                  
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#> [3] /usr/lib/R/site-library
#> [4] /usr/lib/R/library

[2005m]

I am not sure but I think I see where the issue is coming from. We only take into account the attributes of the first argument. We actually have the same problem with fifelse and fcoalesce. I think we need to manage S4 object at C levels.

[2005m]

@torema-ed , thank you very much for reporting this. I will raise it as a feature request. In the meantime I think that we should notify the user (at least for fifelse and fcase) that S4 object are not supported. I will hence raise an issue for that.

[2005m]

@torema-ed , now that #4135 has been closed you should have an error message in your example.

[torema-ed]

@2005m Great, thank you!

I'll leave the decision of closing this issue to you as I'm not too sure if you want to keep it open for future reference.

[2005m]

Thank you @torema-ed , I would leave it open for now in case there are other S4 objects for which fcase is not working. I am also curious to know if there is a real demand for it. Depending on the Rdatatable team we might want to support lubridate in the future or not...it is opened to discussion...