Ian Cook created ARROW-14050:
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Summary: [C++] tdigest, quantile return empty arrays when nulls
not skipped
Key: ARROW-14050
URL: https://issues.apache.org/jira/browse/ARROW-14050
Project: Apache Arrow
Issue Type: New Feature
Components: C++
Affects Versions: 6.0.0
Reporter: Ian Cook
This is a C++ kernel issue, but the examples below use the R bindings to call
the C++ kernels.
The aggregate functions {{tdigest}} and {{quantile}} return arrays with the
same length as the option value {{q}}:
{code:r}
call_function("tdigest", Array$create(c(1, 2, 3, NA)), options = list(q =
c(0.1, 0.9), skip_nulls = TRUE))
## Array
## <double>
## [
## 1,
## 3
## ]{code}
But when the data includes {{null}} values and the option {{skip_nulls}} is set
to {{false}}, these kernels instead return zero-length arrays:
{code:r}
call_function("tdigest", Array$create(c(1, 2, 3, NA)), options = list(q =
c(0.1, 0.9), skip_nulls = FALSE))
## Array
## <double>
## []{code}
This is difficult to handle in bindings; it requires addition of special code
to handle the case where the array comes back empty. It would be much better if
the returned array in this situation had the same length {{q}} with {{null}} in
every position:
{code:r}
## Array
## <double>
## [
## null,
## null
## ] {code}
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