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[REVIEW] Fix usecols parameter handling in dask_cudf.read_csv #9618

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Nov 5, 2021
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[REVIEW] Fix usecols parameter handling in dask_cudf.read_csv #9618

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d682609
fix usecols param usage
galipremsagar Nov 5, 2021
18a9b3e
Update csv.py
galipremsagar Nov 5, 2021
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4 changes: 4 additions & 0 deletions python/dask_cudf/dask_cudf/io/csv.py
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Original file line number Diff line number Diff line change
Expand Up @@ -111,6 +111,7 @@ def _internal_read_csv(path, chunksize="256 MiB", **kwargs):
return read_csv_without_chunksize(path, **kwargs)

dask_reader = make_reader(cudf.read_csv, "read_csv", "CSV")
usecols = kwargs.pop("usecols", None)
meta = dask_reader(filenames[0], **kwargs)._meta

dsk = {}
Expand All @@ -130,11 +131,14 @@ def _internal_read_csv(path, chunksize="256 MiB", **kwargs):
"names"
] = meta.columns # no header in the middle of the file
kwargs2["header"] = None
kwargs2["usecols"] = usecols
dsk[(name, i)] = (apply, _read_csv, [fn, dtypes], kwargs2)

i += 1

divisions = [None] * (len(dsk) + 1)
if usecols is not None:
meta = meta[usecols]
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return dd.core.new_dd_object(dsk, name, meta, divisions)


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16 changes: 16 additions & 0 deletions python/dask_cudf/dask_cudf/io/tests/test_csv.py
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Expand Up @@ -134,3 +134,19 @@ def test_read_csv_chunksize_none(tmp_path, compression, size):
df.to_csv(path, index=False, compression=compression)
df2 = dask_cudf.read_csv(path, chunksize=None, dtype=typ)
dd.assert_eq(df, df2)


def test_csv_reader_usecols(tmp_path):
df = cudf.DataFrame(
{
"a": [1, 2, 3, 4] * 100,
"b": ["a", "b", "c", "d"] * 100,
"c": [10, 11, 12, 13] * 100,
}
)
csv_path = str(tmp_path / "usecols_data.csv")
df.to_csv(csv_path, index=False)
ddf = dask_cudf.from_cudf(df[["b", "c"]], npartitions=5)
ddf2 = dask_cudf.read_csv(csv_path, usecols=["b", "c"])

dd.assert_eq(ddf, ddf2, check_divisions=False, check_index=False)