milesgranger commented on code in PR #14395:
URL: https://github.com/apache/arrow/pull/14395#discussion_r1010272378
##########
cpp/src/arrow/compute/kernels/scalar_nested.cc:
##########
@@ -87,6 +89,206 @@ Status GetListElementIndex(const ExecValue& value, T* out) {
return Status::OK();
}
+template <typename Type, typename IndexType>
+struct ListSlice {
+ using offset_type = typename Type::offset_type;
+
+ static Status Exec(KernelContext* ctx, const ExecSpan& batch, ExecResult*
out) {
+ const auto opts = OptionsWrapper<ListSliceOptions>::Get(ctx);
+
+ // Invariants
+ if (opts.start < 0 || (opts.start >= opts.stop && opts.stop != -1)) {
+ // TODO: support start == stop which should give empty lists
+ return Status::Invalid("`start`(", opts.start,
+ ") should be greater than 0 and smaller than
`stop`(",
+ opts.stop, ")");
+ }
+ if (opts.step != 1) {
+ // TODO: support step in slicing
+ return Status::NotImplemented(
+ "Setting `step` to anything other than 1 is not supported; got
step=",
+ opts.step);
+ }
+ if (opts.stop == -1) {
+ // TODO: Support slicing to arbitrary end
Review Comment:
That sounds good! However I can't seem to get around the conversion of the
options to string in `string_builder` when using the `std::optional<int64_t>`
> /home/milesg/Projects/arrow/cpp/src/arrow/util/string_builder.h:49:10:
error: no match for 'operator<<' (operand types are 'std::ostream' {aka
'std::basic_ostream<char>'} and 'const std::optional<long int>')
49 | stream << head;
| ~~~~~~~^~~~~~~
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