Neville Dipale created ARROW-5352:
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Summary: [Rust] BinaryArray filter loses replaces nulls with empty
strings
Key: ARROW-5352
URL: https://issues.apache.org/jira/browse/ARROW-5352
Project: Apache Arrow
Issue Type: Bug
Components: Rust
Affects Versions: 0.13.0
Reporter: Neville Dipale
The filter implementation for BinaryArray discards nullness of data.
BinaryArrays that are null (seem to) always return an empty string slice when
getting a value, so the way filter works might be a bug depending on what Arrow
developers' or users' intentions are.
I think we should either preserve nulls (and their count) or document this as
intended behaviour.
Below is a test case that reproduces the bug.
{code:java}
#[test]
fn test_filter_binary_array_with_nulls() {
let mut a: BinaryBuilder = BinaryBuilder::new(100);
a.append_null().unwrap();
a.append_string("a string").unwrap();
a.append_null().unwrap();
a.append_string("with nulls").unwrap();
let array = a.finish();
let b = BooleanArray::from(vec![true, true, true, true]);
let c = filter(&array, &b).unwrap();
let d: &BinaryArray = c.as_any().downcast_ref::<BinaryArray>().unwrap();
// I didn't expect this behaviour
assert_eq!("", d.get_string(0));
// fails here
assert!(d.is_null(0));
assert_eq!(4, d.len());
// fails here
assert_eq!(2, d.null_count());
assert_eq!("a string", d.get_string(1));
// fails here
assert!(d.is_null(2));
assert_eq!("with nulls", d.get_string(3));
}
{code}
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