nealrichardson commented on a change in pull request #12533:
URL: https://github.com/apache/arrow/pull/12533#discussion_r818245512
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File path: r/tests/testthat/test-record-batch-reader.R
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@@ -139,3 +139,21 @@ test_that("reader with 0 batches", {
expect_r6_class(tab, "Table")
expect_identical(dim(tab), c(0L, 1L))
})
+
+test_that("reader head method edge cases", {
+ batch <- record_batch(
+ x = 1:10,
+ y = letters[1:10]
+ )
+ sink <- BufferOutputStream$create()
+ writer <- RecordBatchStreamWriter$create(sink, batch$schema)
+ writer$write(batch)
+ writer$write(batch)
+ writer$close()
+ buf <- sink$finish()
+
+ reader <- RecordBatchStreamReader$create(buf)
+ expect_error(head(reader, -1)) # Not (yet) supported
+ expect_equal(head(reader, 0), Table$create(x = integer(0), y = character(0)))
+ expect_equal(head(reader, 100), Table$create(batch, batch))
Review comment:
Actually I believe the opposite is true: the method is consuming the
reader. RecordBatchReader (and Scanner) are one-shot. (I think you may be
misreading the C++ function: `reader` is the reader and we collect into
`batches` via `push_back`, there is no pushing back into `reader`.)
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