[jira] [Created] (ARROW-18101) [R] RecordBatchReaderHead from ExecPlan with UDF cannot be read

["Neal Richardson (Jira)" <ji...@apache.org>]

Neal Richardson created ARROW-18101:
---------------------------------------

             Summary: [R] RecordBatchReaderHead from ExecPlan with UDF cannot be read
                 Key: ARROW-18101
                 URL: https://issues.apache.org/jira/browse/ARROW-18101
             Project: Apache Arrow
          Issue Type: Bug
          Components: R
            Reporter: Neal Richardson


{code}
  register_scalar_function(
    "times_32",
    function(context, x) x * 32.0,
    int32(),
    float64(),
    auto_convert = TRUE
  )
  record_batch(a = 1:1000) %>%
    dplyr::mutate(b = times_32(a)) %>%
    as_record_batch_reader() %>%
    head(11) %>%
    as_arrow_table()

# Error: NotImplemented: Call to R (resolve scalar user-defined function output data type) from a non-R thread from an unsupported context
# /arrow/cpp/src/arrow/compute/exec.cc:649  kernel_->signature->out_type().Resolve(kernel_ctx_, args.inputs)
# /arrow/cpp/src/arrow/compute/exec/expression.cc:602  executor->Init(&kernel_context, {kernel, types, options})
# /arrow/cpp/src/arrow/compute/exec/project_node.cc:91  ExecuteScalarExpression(simplified_expr, target, plan()->exec_context())
# /arrow/cpp/src/arrow/record_batch.cc:336  ReadNext(&batch)
# /arrow/cpp/src/arrow/record_batch.cc:350  ToRecordBatches()
{code}

It works fine if you don't call {{as_record_batch_reader()}} in the middle. Oddly, it also works fine if you add {{as_adq()}} (aka {{collapse()}}) after head() and before evaluating to table--that is, if you run it through an ExecPlan again, it doesn't error.



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