[jira] [Created] (ARROW-14050) [C++] tdigest, quantile return empty arrays when nulls not skipped

["Ian Cook (Jira)" <ji...@apache.org>]

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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