[jira] [Created] (ARROW-16503) [C++] Can't concatenate extension arrays

["Dewey Dunnington (Jira)" <ji...@apache.org>]

Dewey Dunnington created ARROW-16503:
----------------------------------------

             Summary: [C++] Can't concatenate extension arrays
                 Key: ARROW-16503
                 URL: https://issues.apache.org/jira/browse/ARROW-16503
             Project: Apache Arrow
          Issue Type: Improvement
          Components: C++
            Reporter: Dewey Dunnington


It looks like Arrays with an extension type can't be concatenated. From the R bindings:

{code:R}
library(arrow, warn.conflicts = FALSE)

arr <- vctrs_extension_array(1:10)
concat_arrays(arr, arr)
#> Error: NotImplemented: concatenation of integer(0)
#> /Users/deweydunnington/Desktop/rscratch/arrow/cpp/src/arrow/array/concatenate.cc:195  VisitTypeInline(*out_->type, this)
#> /Users/deweydunnington/Desktop/rscratch/arrow/cpp/src/arrow/array/concatenate.cc:590  ConcatenateImpl(data, pool).Concatenate(&out_data)
{code}

This shows up more practically when using the query engine:

{code:R}
library(arrow, warn.conflicts = FALSE)

table <- arrow_table(
  group = rep(c("a", "b"), 5),
  col1 = 1:10,
  col2 = vctrs_extension_array(1:10)
)

tf <- tempfile()
table |> dplyr::group_by(group) |> write_dataset(tf)
open_dataset(tf) |>
  dplyr::arrange(col1) |> 
  dplyr::collect()
#> Error in `dplyr::collect()`:
#> ! NotImplemented: concatenation of extension<arrow.r.vctrs>
#> /Users/deweydunnington/Desktop/rscratch/arrow/cpp/src/arrow/array/concatenate.cc:195  VisitTypeInline(*out_->type, this)
#> /Users/deweydunnington/Desktop/rscratch/arrow/cpp/src/arrow/array/concatenate.cc:590  ConcatenateImpl(data, pool).Concatenate(&out_data)
#> /Users/deweydunnington/Desktop/rscratch/arrow/cpp/src/arrow/compute/kernels/vector_selection.cc:2025  Concatenate(values.chunks(), ctx->memory_pool())
#> /Users/deweydunnington/Desktop/rscratch/arrow/cpp/src/arrow/compute/kernels/vector_selection.cc:2084  TakeCA(*table.column(j), indices, options, ctx)
#> /Users/deweydunnington/Desktop/rscratch/arrow/cpp/src/arrow/compute/exec/sink_node.cc:527  impl_->DoFinish()
#> /Users/deweydunnington/Desktop/rscratch/arrow/cpp/src/arrow/compute/exec/exec_plan.cc:467  iterator_.Next()
#> /Users/deweydunnington/Desktop/rscratch/arrow/cpp/src/arrow/record_batch.cc:337  ReadNext(&batch)
#> /Users/deweydunnington/Desktop/rscratch/arrow/cpp/src/arrow/record_batch.cc:351  ToRecordBatches()
{code}




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