alamb commented on code in PR #6252:
URL: https://github.com/apache/arrow-rs/pull/6252#discussion_r1725057031
##########
parquet/src/arrow/array_reader/primitive_array.rs:
##########
@@ -217,35 +217,19 @@ where
arrow_cast::cast(&a, target_type)?
}
ArrowType::Decimal128(p, s) => {
- // We can simply reuse the null buffer from `array` rather
than recomputing it
- // (as was the case when we simply used `collect` to produce
the new array).
- let nulls = array.nulls().cloned();
let array = match array.data_type() {
- ArrowType::Int32 => {
- let decimal = array
- .as_any()
- .downcast_ref::<Int32Array>()
- .unwrap()
- .iter()
- .map(|v| match v {
- Some(i) => i as i128,
- None => i128::default(),
- });
- Decimal128Array::from_iter_values_with_nulls(decimal,
nulls)
- }
-
- ArrowType::Int64 => {
- let decimal = array
- .as_any()
- .downcast_ref::<Int64Array>()
- .unwrap()
- .iter()
- .map(|v| match v {
- Some(i) => i as i128,
- None => i128::default(),
- });
- Decimal128Array::from_iter_values_with_nulls(decimal,
nulls)
- }
+ ArrowType::Int32 => array
Review Comment:
I suggest we add a comment explaining the rationale for not checking nulls
-- something like
```rust
// Apply conversion to all elements regardless of null slots as the
conversion
// to `i128` is infallible. This improves performance by avoiding a branch
in
// the inner loop
```
##########
arrow-array/src/array/primitive_array.rs:
##########
@@ -1016,6 +1016,36 @@ impl<T: ArrowPrimitiveType> PrimitiveArray<T> {
PrimitiveArray::new(values, Some(nulls))
}
+ /// Applies a unary infallible function to each value in an array,
producing a
+ /// new primitive array.
+ ///
+ /// # Null Handling
+ ///
+ /// See [`Self::unary`] for more information on null handling.
+ ///
+ /// # Example: create an [`Int16Array`] from an [`ArrayAccessor`] with
item type `&[u8]`
+ /// ```
+ /// use arrow_array::{Array, FixedSizeBinaryArray, Int16Array};
+ /// let input_arg = vec![ vec![1, 0], vec![2, 0], vec![3, 0] ];
+ /// let arr =
FixedSizeBinaryArray::try_from_iter(input_arg.into_iter()).unwrap();
+ /// let c = Int16Array::from_unary(&arr, |x|
i16::from_le_bytes(x[..2].try_into().unwrap()));
+ /// assert_eq!(c, Int16Array::from(vec![Some(1i16), Some(2i16),
Some(3i16)]));
+ /// ```
+ pub fn from_unary<U: ArrayAccessor, F>(left: U, mut op: F) -> Self
Review Comment:
I like how this follows the model of `BooleanArray::from_unary`
https://docs.rs/arrow/latest/arrow/array/struct.BooleanArray.html#method.from_unary
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