[GitHub] [arrow] djnavarro commented on pull request #12154: ARROW-14821: [R] Implement bindings for lubridate's floor_date, ceiling_date, and round_date

[GitBox <gi...@apache.org>]

djnavarro commented on pull request #12154:
URL: https://github.com/apache/arrow/pull/12154#issuecomment-1014161114


   I think I've taken this as far as I can right now? I had been hoping to write shims to support the `week_start` and `change_on_boundary` arguments but I'm not sure if that's possible right now. My original thought was to try something like this:
   
   ```r
   week_start_shim <- function(function_name, x, week_start, opts) {
     offset <- Expression$create(Scalar$create(as.difftime(week_start - 4, units = "days")))
     x <- Expression$create("add", x, offset)
     x <- Expression$create(function_name, x, options = opts)
     return(Expression$create("subtract", x, offset)
   } 
   ```
   
   I can't get anything like this to work because (as far as I can tell) we don't currently have the ability to add or subtract durations from date/time in Arrow. I imagine I'm missing something obvious here! 
   
   


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