edponce commented on code in PR #13009:
URL: https://github.com/apache/arrow/pull/13009#discussion_r859921831
##########
cpp/src/arrow/stl_iterator.h:
##########
@@ -128,6 +131,215 @@ class ArrayIterator {
int64_t index_;
};
+template <typename ArrayType,
+ typename ValueAccessor = detail::DefaultValueAccessor<ArrayType>>
+class ChunkedArrayIterator {
+ public:
+ using value_type = arrow::util::optional<typename ValueAccessor::ValueType>;
+ using difference_type = int64_t;
+ using pointer = value_type*;
+ using reference = value_type&;
+ using iterator_category = std::random_access_iterator_tag;
+
+ // Some algorithms need to default-construct an iterator
+ ChunkedArrayIterator() : chunked_array_(NULLPTR), index_(0),
current_chunk_index_(0) {}
+
+ explicit ChunkedArrayIterator(const ChunkedArray& chunked_array, int64_t
index = 0)
+ : chunked_array_(&chunked_array), index_(index) {
+ InitializeComponents(*this);
+ }
+
+ // Value access
+ value_type operator*() const { return
*iterators_list_[current_chunk_index_]; }
+
+ value_type operator[](difference_type n) const {
+ int64_t chunk_index = GetChunkIndex(index_ + n);
+ int64_t index_in_chunk =
+ chunk_index ? index_ + n - chunks_lengths_[chunk_index - 1] : index_ +
n;
+ return iterators_list_[chunk_index]
+ [index_in_chunk -
iterators_list_[chunk_index].index()];
Review Comment:
[`ChunkedArray` already has
`GetScalar(index)`](https://github.com/apache/arrow/blob/master/cpp/src/arrow/chunked_array.h#L145)
which is efficient for accessing sequential scalars at particular logical
indices. I suggest to use it for the iteration. There is no need to perform
complex index calculations/checks in the iterator. This would be somewhat
analogous to the [`Array`
iterator`](https://github.com/apache/arrow/blob/master/cpp/src/arrow/stl_iterator.h#L61-L67).
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