paleolimbot commented on code in PR #12817:
URL: https://github.com/apache/arrow/pull/12817#discussion_r854103665
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r/R/array.R:
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@@ -217,6 +217,125 @@ Array$create <- function(x, type = NULL) {
Array$import_from_c <- ImportArray
+#' Convert an object to an Arrow Array
+#'
+#' Whereas `Array$create()` constructs an [Array] from the built-in data types
+#' for which the Arrow package implements fast converters, `as_arrow_array()`
+#' provides a means by which other packages can define conversions to Arrow
+#' objects.
+#'
+#' @param x An object to convert to an Arrow Array
+#' @param ... Passed to S3 methods
+#' @param type A [type][data-type] for the final Array. A value of `NULL`
+#' will default to the type guessed by [type()].
+#'
+#' @return An [Array].
+#' @export
+#'
+#' @examplesIf arrow_available()
+#' as_arrow_array(1:5)
+#'
+as_arrow_array <- function(x, ..., type = NULL) {
+ UseMethod("as_arrow_array")
+}
+
+#' @rdname as_arrow_array
+#' @export
+as_arrow_array.Array <- function(x, ..., type = NULL) {
+ if (is.null(type)) {
+ x
+ } else {
+ x$cast(type)
+ }
+}
+
+#' @rdname as_arrow_array
+#' @export
+as_arrow_array.ChunkedArray <- function(x, ..., type = NULL) {
+ concat_arrays(!!! x$chunks, type = type)
+}
+
+#' @rdname as_arrow_array
+#' @export
+as_arrow_array.vctrs_vctr <- function(x, ..., type = NULL) {
+ if (is.null(type)) {
+ vctrs_extension_array(x)
+ } else if (inherits(type, "VctrsExtensionType")) {
+ vctrs_extension_array(
+ x,
+ ptype = type$ptype(),
+ storage_type = type$storage_type()
+ )
+ } else {
+ stop_cant_convert_array(x, type)
Review Comment:
Because you were right about the possibility of infinite loops! We sometimes
try the S3 methods first (i.e., when calling `as_arrow_array()`) and sometimes
try C++ conversion first (e.g., when calling `Table$create()`)...I found it a
bit easier to predict what will happen if we always just stop when conversion
isn't possible.
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