velvia commented on a change in pull request #8688:
URL: https://github.com/apache/arrow/pull/8688#discussion_r530547648
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File path: rust/arrow/src/compute/kernels/boolean.rs
##########
@@ -223,6 +224,101 @@ pub fn is_not_null(input: &Array) -> Result<BooleanArray>
{
Ok(BooleanArray::from(Arc::new(data)))
}
+/// Copies original array, setting null bit to true if a secondary comparison
boolean array is set to true.
+/// Typically used to implement NULLIF.
+// NOTE: For now this only supports Primitive Arrays. Although the code could
be made generic, the issue
+// is that currently the bitmap operations result in a final bitmap which is
aligned to bit 0, and thus
+// the left array's data needs to be sliced to a new offset, and for
non-primitive arrays shifting the
+// data might be too complicated. In the future, to avoid shifting left
array's data, we could instead
+// shift the final bitbuffer to the right, prepending with 0's instead.
+pub fn nullif<T>(
+ left: &PrimitiveArray<T>,
+ right: &BooleanArray,
+) -> Result<PrimitiveArray<T>>
+where
+ T: ArrowNumericType,
+{
+ if left.len() != right.len() {
+ return Err(ArrowError::ComputeError(
+ "Cannot perform comparison operation on arrays of different length"
+ .to_string(),
+ ));
+ }
+ let left_data = left.data();
+ let right_data = right.data();
+
+ // If left has no bitmap, create a new one with all values set for nullity
op later
+ // left=0 (null) right=null output bitmap=null
+ // left=0 right=1 output bitmap=null
+ // left=1 (set) right=null output bitmap=set (passthrough)
+ // left=1 right=1 & comp=true output bitmap=null
+ // left=1 right=1 & comp=false output bitmap=set
+ //
+ // Thus: result = left null bitmap & (!right_values | !right_bitmap)
+ // OR left null bitmap & !(right_values & right_bitmap)
+ //
+ // Do the right expression !(right_values & right_bitmap) first since
there are two steps
+ // TRICK: convert BooleanArray buffer as a bitmap for faster operation
+ let right_combo_buffer = match right.data().null_bitmap() {
+ Some(right_bitmap) => {
+ // NOTE: right values and bitmaps are combined and stay at bit
offset right.offset()
+ (&right.values() & &right_bitmap.bits).ok().map(|b| b.not())
+ }
+ None => Some(!&right.values()),
+ };
+
+ // AND of original left null bitmap with right expression
+ // Here we take care of the possible offsets of the left and right arrays
all at once.
+ let modified_null_buffer = match left_data.null_bitmap() {
+ Some(left_null_bitmap) => match right_combo_buffer {
+ Some(rcb) => Some(buffer_bin_and(
+ &left_null_bitmap.bits,
+ left_data.offset(),
+ &rcb,
+ right_data.offset(),
+ left_data.len(),
+ )),
+ None => Some(
+ left_null_bitmap
+ .bits
+ .bit_slice(left_data.offset(), left.len()),
+ ),
+ },
+ None => right_combo_buffer,
Review comment:
Ah yes, thanks.
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