feat: export $arr$to_list() (#1018)

NEWS.md

@@ -109,6 +109,7 @@
 - New functions `pl$int_range()` and `pl$int_ranges()` (#968).
 - New string method `$str$extract_groups()` (#979).
 - New string method `$str$find()` (#985).
+- New array method `$arr$to_list()` (#1018).
 - New argument `n` in `$str$replace()` (#987).
 - Method `$over()` gains an argument `mapping_strategy` (#984, #988).
 - New method `$item()` for `DataFrame` and `Series` (#992).

R/expr__array.R

@@ -278,6 +278,22 @@ ExprArr_shift = function(periods = 1) {
     unwrap("in $arr$shift():")
 }
 
+
+#' Convert an Array column into a List column with the same inner data type
+#'
+#' @return [Expr][Expr_class] of [data type List][DataType_List]
+#' @examples
+#' df = pl$DataFrame(
+#'   a = list(c(1, 2), c(3, 4)),
+#'   schema = list(a = pl$Array(pl$Int8, 2))
+#' )
+#'
+#' df$with_columns(
+#'   list = pl$col("a")$arr$to_list()
+#' )
+ExprArr_to_list = function() .pr$Expr$arr_to_list(self)
+
+
 #' Convert array to struct
 #'
 #' @inheritParams ExprList_to_struct

tests/testthat/test-expr_array.R

@@ -300,6 +300,22 @@ test_that("arr$shift", {
   )
 })
 
+test_that("arr$to_list", {
+  df = pl$DataFrame(
+    strings = list(c("a", "b"), c("c", "d")),
+    schema = list(strings = pl$Array(pl$String, 2))
+  )
+
+  expect_true(
+    df$select(pl$col("strings")$arr$to_list())$equals(
+      pl$DataFrame(
+        strings = list(c("a", "b"), c("c", "d")),
+        schema = list(strings = pl$List(pl$String))
+      )
+    )
+  )
+})
+
 test_that("arr$to_struct", {
   df = pl$DataFrame(
     strings = list(c("a", "b"), c("c", "d")),