milesgranger commented on code in PR #14395:
URL: https://github.com/apache/arrow/pull/14395#discussion_r1013794685
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cpp/src/arrow/compute/kernels/scalar_nested.cc:
##########
@@ -87,6 +89,195 @@ 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.stop.has_value()) {
+ // TODO: Support slicing to arbitrary end
+ // For variable size list, this would be the largest difference in
offsets
+ // For fixed size list, this would be the fixed size.
+ return Status::NotImplemented(
+ "Slicing to end not yet implemented, please set `stop` parameter.");
+ }
+ if (opts.start < 0 || opts.start >= opts.stop.value()) {
+ // 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);
+ }
+
+ const ArraySpan& list_ = batch[0].array;
+ const Type* list_type = checked_cast<const Type*>(list_.type);
+ const auto value_type = list_type->value_type();
+
+ std::unique_ptr<ArrayBuilder> builder;
+
+ // construct array values
+ if (opts.return_fixed_size_list) {
+ RETURN_NOT_OK(MakeBuilder(
+ ctx->memory_pool(),
+ fixed_size_list(value_type,
+ static_cast<int32_t>(opts.stop.value() -
opts.start)),
+ &builder));
+ RETURN_NOT_OK(BuildArray<FixedSizeListBuilder>(batch, opts, *builder));
+ } else {
+ if constexpr (std::is_same_v<Type, LargeListType>) {
+ RETURN_NOT_OK(MakeBuilder(ctx->memory_pool(), large_list(value_type),
&builder));
+ RETURN_NOT_OK(BuildArray<LargeListBuilder>(batch, opts, *builder));
+ } else {
+ RETURN_NOT_OK(MakeBuilder(ctx->memory_pool(), list(value_type),
&builder));
Review Comment:
As mentioned in
https://github.com/apache/arrow/pull/14395/commits/8a3bc6d2e7a3f051bad2b26536711d8a89b10e25,
it seems, naively, the field names are preserved?
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