[GitHub] [arrow-rs] Jimexist commented on a change in pull request #386: add more tests for window::shift and handle boundary cases

[GitBox <gi...@apache.org>]

Jimexist commented on a change in pull request #386:
URL: https://github.com/apache/arrow-rs/pull/386#discussion_r643959521



##########
File path: arrow/src/compute/kernels/window.rs
##########
@@ -33,56 +32,120 @@ use crate::{array::PrimitiveArray, datatypes::ArrowPrimitiveType, error::Result}
 /// use arrow::compute::shift;
 ///
 /// let a: Int32Array = vec![Some(1), None, Some(4)].into();
+///
 /// // shift array 1 element to the right
 /// let res = shift(&a, 1).unwrap();
 /// let expected: Int32Array = vec![None, Some(1), None].into();
-/// assert_eq!(res.as_ref(), &expected)
+/// assert_eq!(res.as_ref(), &expected);
+///
+/// // shift array 1 element to the left
+/// let res = shift(&a, -1).unwrap();
+/// let expected: Int32Array = vec![None, Some(4), None].into();
+/// assert_eq!(res.as_ref(), &expected);
+///
+/// // shift array 0 element, although not recommended
+/// let res = shift(&a, 0).unwrap();
+/// let expected: Int32Array = vec![Some(1), None, Some(4)].into();
+/// assert_eq!(res.as_ref(), &expected);
+///
+/// // shift array 3 element tot he right
+/// let res = shift(&a, 3).unwrap();
+/// let expected: Int32Array = vec![None, None, None].into();
+/// assert_eq!(res.as_ref(), &expected);
 /// ```
 pub fn shift<T>(values: &PrimitiveArray<T>, offset: i64) -> Result<ArrayRef>
 where
     T: ArrowPrimitiveType,
 {
-    // Compute slice
-    let slice_offset = clamp(-offset, 0, values.len() as i64) as usize;
-    let length = values.len() - abs(offset) as usize;
-    let slice = values.slice(slice_offset, length);
-
-    // Generate array with remaining `null` items
-    let nulls = abs(offset as i64) as usize;
+    let value_len = values.len() as i64;
+    if offset == 0 {
+        Ok(values.slice(0, values.len()))

Review comment:
       i guess it's not that easy - there's no easy way to clone array and likely suboptimal than just taking a slice here




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