nealrichardson commented on code in PR #19706:
URL: https://github.com/apache/arrow/pull/19706#discussion_r1072593608
##########
r/R/expression.R:
##########
@@ -89,6 +92,56 @@ Expression$create <- function(function_name,
expr
}
+
+#' @export
+`[[.Expression` <- function(x, i, ...) {
+ # TODO: integer (positional) field refs are supported in C++
+ assert_that(is.string(i))
+ get_nested_field(x, i)
+}
+
+#' @export
+`$.Expression` <- function(x, name, ...) {
+ assert_that(is.string(name))
+ if (name %in% ls(x)) {
+ get(name, x)
+ } else {
+ get_nested_field(x, name)
+ }
+}
+
+get_nested_field <- function(expr, name) {
+ if (expr$is_field_ref()) {
+ # Make a nested field ref
+ out <- compute___expr__nested_field_ref(expr, name)
+ } else {
+ # Use the struct_field kernel, but that only works if:
+ # * expr has a knowable type (has a schema set)
+ # * that type is struct
+ # * `name` exists in the struct (bc we have to map to an integer position)
Review Comment:
Good to know, I can update to use that. Seems that
https://arrow.apache.org/docs/dev/cpp/compute.html#cpp-compute-vector-structural-transforms
is outdated and should be updated to reflect that.
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