romainfrancois commented on a change in pull request #10730:
URL: https://github.com/apache/arrow/pull/10730#discussion_r672174111
##########
File path: r/src/array_to_vector.cpp
##########
@@ -69,13 +69,25 @@ class Converter {
// special case when there is only one array
if (chunked_array_->num_chunks() == 1) {
const auto& array = chunked_array_->chunk(0);
- if (arrow::r::GetBoolOption("arrow.use_altrep", true) && array->length()
> 0 &&
- array->null_count() == 0) {
+ // using altrep if
+ // - the arrow.use_altrep is set to TRUE or unset
+ // - the array has at least one element
+ // - either it has no nulls or the data is mutable
+ if (arrow::r::GetBoolOption("arrow.use_altrep", true) && array->length()
> 0) {
switch (array->type()->id()) {
case arrow::Type::DOUBLE:
- return arrow::r::MakeDoubleArrayNoNull(array);
+ if (array->null_count() == 0 ||
array->data()->buffers[1]->is_mutable()) {
Review comment:
One consequence is that we can't use altrep when taking slices of an
Array as the buffer is at least held by two Arrays then.
``` r
library(arrow, warn.conflicts = FALSE)
#> See arrow_info() for available features
is_altrep <- arrow:::is_altrep
v_int <- Array$create(c(1L, NA, 3L))
is_altrep(v_int$as_vector())
#> [1] TRUE
is_altrep(as.vector(v_int$Slice(1)))
#> [1] FALSE
```
<sup>Created on 2021-07-19 by the [reprex
package](https://reprex.tidyverse.org) (v2.0.0)</sup>
I commented out the relevant tests in `test-altrep.R`. Does this matter
given that the data there is irrelevant because it's identified as null ?
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