wjones127 commented on code in PR #15210:
URL: https://github.com/apache/arrow/pull/15210#discussion_r1064886810
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cpp/src/arrow/array/array_list_test.cc:
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@@ -509,6 +509,18 @@ class TestListArray : public ::testing::Test {
ASSERT_RAISES(Invalid, ValidateOffsets(2, {0, 7, 4}, values));
}
+ void TestSliced() {
+ auto arr = ArrayFromJSON(list(int16()), "[[1, 2], [3, 4, 5], [6], [7,
8]]");
+
+ auto arr_sliced = arr->Slice(0, 2);
+ auto expected_sliced = ArrayFromJSON(list(int16()), "[[1, 2], [3, 4, 5]]");
+ AssertArraysEqual(*expected_sliced, *arr_sliced);
+
+ auto values = checked_cast<ListArray*>(arr_sliced.get())->values();
+ auto expected_values = ArrayFromJSON(int16(), "[1, 2, 3, 4, 5]");
+ AssertArraysEqual(*expected_values, *values);
Review Comment:
> Because we use the offsets to slice into the flat values, and those
offsets take into account potential values behind a null?
Oh now I remember, and I think I understand what you are saying here better
now. For the fixed size lists, the values behind a null entry in the list are
removed when we call `Flatten()`. When we go back to try to reconstruct the
lists based on offsets, the offsets produced by `value_offset` are all invalid
since they don't account for the values we dropped in `Flatten()`.
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