jorgecarleitao commented on a change in pull request #8541:
URL: https://github.com/apache/arrow/pull/8541#discussion_r517095720
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File path: rust/arrow/src/array/data.rs
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@@ -207,6 +210,56 @@ impl ArrayData {
size
}
+
+ /// Creates a zero-copy slice of itself. This creates a new [ArrayData]
+ /// with a different offset, len and a shifted null bitmap.
+ ///
+ /// # Panics
+ ///
+ /// Panics if `offset + length > self.len()`.
+ pub fn slice(&self, offset: usize, length: usize) -> ArrayData {
+ assert!((offset + length) <= self.len());
+
+ let mut new_data = self.clone();
+
+ new_data.len = length;
+ new_data.offset = offset + self.offset;
+
+ new_data.null_count =
+ count_nulls(new_data.null_buffer(), new_data.offset, new_data.len);
+
+ new_data
+ }
+
+ /// Returns the buffer `buffer` as a slice of type `T`. When the expected
buffer is bit-packed,
+ /// the slice is not offset.
+ #[inline]
+ pub(super) fn buffer<T>(&self, buffer: usize) -> &[T] {
+ let values = unsafe { self.buffers[buffer].data().align_to::<T>() };
+ if values.0.len() != 0 || values.2.len() != 0 {
+ panic!("The buffer is not byte-aligned with its interpretation")
+ };
+ if self.data_type.width(buffer).unwrap() == 1 {
+ // bitpacked buffers are offset differently and it is the
consumers that need to worry about.
+ &values.1
+ } else {
+ &values.1[self.offset..]
+ }
+ }
+
+ /// Returns the buffer `buffer` as a slice of type `T`. When the expected
buffer is bit-packed,
+ /// the slice is not offset.
+ #[inline]
+ pub fn buffer_data(&self, buffer: usize) -> &[u8] {
+ let values = self.buffers[buffer].data();
+ let width = self.data_type.width(buffer).unwrap();
+ if width == 1 {
+ // bitpacked buffers are offset differently and it is the
consumers that need to worry about.
+ &values
+ } else {
+ &values[self.offset * (width / 8)..]
+ }
+ }
}
impl PartialEq for ArrayData {
Review comment:
One Idea would be to use the equality code from this PR, but sprinkle it
with `debug_assert_eq`, so that during debug, it is more clear where the
difference is. An alternative is to use `assert_eq`, so that the two arrays are
shown side-by-side (this only works for small arrays, though).
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