sgilmore10 opened a new pull request, #47116:
URL: https://github.com/apache/arrow/pull/47116
### Rationale for this change
It would be nice if there was a `NumNulls` property on the
`arrow.array.Array` base class. Currently, the only way to figure out the
number of nulls is count the number of `false` values in the `Valid` array:
```matlab
>> a = arrow.array([1 2 NaN 4 5 6 NaN 8 9 10 NaN]);
>> invalidValues = ~a.Valid;
>> numNulls = nnz(invalidValues)
numNulls =
3
```
It would be nice if `NumNulls` was already a property on the array class. As
@kou mentioned, we can use the `arrow::Array::null_count()` to get the number
of nulls.
### What changes are included in this PR?
Added `NumNulls` as a property of the `arrow.array.Array` abstract class.
`NumNulls` is a scalar `int64` value that returns the number of null elements
in the array.
**Example Usage**
```matlab
>> a = arrow.array([1 2 NaN 3 4 NaN 5 6 NaN])
a =
Float64Array with 9 elements and 3 null values:
1 | 2 | null | ... | 5 | 6 | null
>> a.NumNulls
ans =
int64
3
```
### Are these changes tested?
Yes. Added test cases verifying the `NumNulls` property to these MATLAB test
classes: `hNumeric`, `tBooleanArray`, `tTimestampArray`, `tTime32Array`,
`tTime64Array`, `tDate32Array`, `tDate64Array`, `tListArray`, `tStringArray`,
and `tStructArray`.
### Are there any user-facing changes?
Yes. Users can now use the `NumNulls` property to query the number of null
elements in an array.
### Future Changes
1. Add `NumNulls` as a property of `arrow.array.ChunkedArray`.
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