[GitHub] [arrow] romainfrancois commented on a change in pull request #8150: ARROW-9271: [R] Preserve data frame metadata in round trip

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

romainfrancois commented on a change in pull request #8150:
URL: https://github.com/apache/arrow/pull/8150#discussion_r486191107



##########
File path: r/R/record-batch.R
##########
@@ -278,7 +278,10 @@ as.data.frame.RecordBatch <- function(x, row.names = NULL, optional = FALSE, ...
 apply_arrow_r_metadata <- function(x, r_metadata) {
   tryCatch({
     if (!is.null(r_metadata$attributes)) {
-      attributes(x) <- r_metadata$attributes
+      attributes(x)[names(r_metadata$attributes)] <- r_metadata$attributes
+      if (inherits(x, "POSIXlt")) {
+        attr(x, "row.names") <- NULL

Review comment:
       Perhaps this would be better handled by converting the POSIXlt to a Timestamp array rather than a struct type, because on the way back the struct type makes a data frame which needs the `row.names` attribute. 
   
   ``` r
   library(arrow, warn.conflicts = TRUE)
   
   example_with_times <- tibble::tibble(
     posixlt = as.POSIXlt(lubridate::ymd_hms("2018-10-07 19:04:05") + 1:10),
   )
   rb <- record_batch(example_with_times)
   
   attributes(as.data.frame(rb)$posixlt)
   #> $row.names
   #>  [1]  1  2  3  4  5  6  7  8  9 10
   #> 
   #> $names
   #> [1] "sec"   "min"   "hour"  "mday"  "mon"   "year"  "wday"  "yday"  "isdst"
   #> 
   #> $class
   #> [1] "POSIXlt" "POSIXt" 
   #> 
   #> $tzone
   #> [1] "UTC"
   attributes(example_with_times$posixlt)
   #> $names
   #> [1] "sec"   "min"   "hour"  "mday"  "mon"   "year"  "wday"  "yday"  "isdst"
   #> 
   #> $class
   #> [1] "POSIXlt" "POSIXt" 
   #> 
   #> $tzone
   #> [1] "UTC"
   ```
   
   <sup>Created on 2020-09-10 by the [reprex package](https://reprex.tidyverse.org) (v0.3.0.9001)</sup>




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