paleolimbot commented on a change in pull request #12324:
URL: https://github.com/apache/arrow/pull/12324#discussion_r807192866
##########
File path: r/tests/testthat/test-Array.R
##########
@@ -989,6 +989,75 @@ test_that("auto int64 conversion to int can be disabled
(ARROW-10093)", {
})
})
+test_that("concat_arrays works", {
+ concat_empty <- concat_arrays()
+ expect_true(concat_empty$type == null())
+ expect_equal(concat_empty$length(), 0L)
Review comment:
In R, `vctrs::vec_c()` returns `NULL`, which can be inserted into
another `vec_c()` call without affecting the (type or size of the) result. A
`null()` of length 0 works similarly in Arrow (it can be cast to any type).
It's nice when programming (for the same reason that `all(logical(0))` is
`TRUE`).
``` r
library(arrow, warn.conflicts = FALSE)
library(vctrs, warn.conflicts = FALSE)
some_user_input1 <- list()
some_user_input2 <- list()
result_of_some_op <- concat_arrays(!!! some_user_input1, !!!
some_user_input2)
some_user_input <- list(1L, 2:4)
(final_result <- concat_arrays(!!! some_user_input, result_of_some_op, type
= int32()))
#> Array
#> <int32>
#> [
#> 1,
#> 2,
#> 3,
#> 4
#> ]
```
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