[GitHub] [arrow] thisisnic commented on a change in pull request #10269: ARROW-11705: [R] Support scalar value recycling in RecordBatch/Table$create()

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thisisnic commented on a change in pull request #10269:
URL: https://github.com/apache/arrow/pull/10269#discussion_r647568522



##########
File path: r/R/util.R
##########
@@ -110,3 +110,36 @@ handle_embedded_nul_error <- function(e) {
   }
   stop(e)
 }
+
+#' Take an object of length 1 and repeat it.
+#' 
+#' @param object Object of length 1 to be repeated - vector, `Scalar`, `Array`, or `ChunkedArray`
+#' @param n Number of repetitions
+#' 
+#' @return `Array` of length `n`
+#' 
+#' @keywords internal
+repeat_value_as_array <- function(object, n) {
+  if (inherits(object, "ChunkedArray")) {
+    return(MakeArrayFromScalar(Scalar$create(object$chunks[[1]]), n))
+  }
+  return(MakeArrayFromScalar(Scalar$create(object), n))
+}
+
+#' Recycle scalar values in a list of arrays
+#' 
+#' @param arrays List of arrays
+#' @return List of arrays with any vector/Scalar/Array/ChunkedArray values of length 1 recycled 
+#' @keywords internal
+recycle_scalars <- function(arrays){
+  # Get lengths of items in arrays
+  is_df <- map_lgl(arrays, ~inherits(.x, "data.frame"))
+  arr_lens <- lengths(arrays)
+  arr_lens[is_df] <- map_int(arrays[is_df], nrow)
+  
+  if (length(arrays) > 1 && any(arr_lens == 1) && !all(arr_lens==1)) {
+    max_array_len <- max(arr_lens)
+    arrays[arr_lens == 1 & !is_df] <- lapply(arrays[arr_lens == 1 & !is_df], repeat_value_as_array, max_array_len)

Review comment:
       I've now ended up removing this extra code to try to handle mixed length tibble/data.frames as it seems like a lot of effort for something that doesn't seem to be a particularly common use case.  I've added in an error message for if the input tables are tibbles of different lengths.




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