stuartcarnie commented on code in PR #2251:
URL: https://github.com/apache/arrow-rs/pull/2251#discussion_r934957161
##########
arrow/src/compute/kernels/cast.rs:
##########
@@ -1584,6 +1625,303 @@ fn cast_string_to_date64<Offset: OffsetSizeTrait>(
Ok(Arc::new(array) as ArrayRef)
}
+fn seconds_since_midnight(time: &chrono::NaiveTime) -> i32 {
+ let sec = time.num_seconds_from_midnight();
+ let frac = time.nanosecond();
+ let adjust = if frac < 1_000_000_000 { 0 } else { 1 };
+ (sec + adjust) as i32
+}
+
+fn milliseconds_since_midnight(time: &chrono::NaiveTime) -> i32 {
+ /// The number of nanoseconds per millisecond.
+ const NANOS_PER_MILLI: u32 = 1_000_000;
+ /// The number of milliseconds per second.
+ const MILLIS_PER_SEC: u32 = 1_000;
+
+ let sec = time.num_seconds_from_midnight() * MILLIS_PER_SEC;
+ let frac = time.nanosecond();
+ let (frac, adjust) = if frac < 1_000_000_000 {
+ (frac, 0)
+ } else {
+ (frac - 1_000_000_000, MILLIS_PER_SEC)
+ };
+ (sec + adjust + frac / NANOS_PER_MILLI) as i32
+}
+
+/// Casts generic string arrays to `Time32SecondArray`
+fn cast_string_to_time32second<Offset: OffsetSizeTrait>(
+ array: &dyn Array,
+ cast_options: &CastOptions,
+) -> Result<ArrayRef> {
+ let string_array = array
+ .as_any()
+ .downcast_ref::<GenericStringArray<Offset>>()
+ .unwrap();
+
+ let array = if cast_options.safe {
+ let iter = (0..string_array.len()).map(|i| {
+ if string_array.is_null(i) {
+ None
+ } else {
+ string_array
+ .value(i)
+ .parse::<chrono::NaiveTime>()
+ .map(|time| seconds_since_midnight(&time))
+ .ok()
+ }
+ });
Review Comment:
I tried, but unfortunately it fails at runtime with a panic:
```
thread 'compute::kernels::cast::tests::test_cast_string_to_time32second'
panicked at 'trusted_len_unzip requires an upper limit',
arrow/src/array/array_primitive.rs:470:25
```
at
https://github.com/apache/arrow-rs/blob/91b2d7e66b066d54035774625b29ff226c755172/arrow/src/array/array_primitive.rs#L469-L470
The previous `iter` was ultimately of type `Range<usize>`, which returns
`Some(_)` for the `size_hint`:
https://github.com/rust-lang/rust/blob/fe3342816a282949f014caa05ea2e669ff9d3d3c/library/core/src/iter/range.rs#L714-L722
whereas our new `iter` does not, as it does not know the size.
There are probably good reasons, but it is unfortunate that `size_hint` was
not a separate trait, so this could be caught at compile time.
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