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Clarify CoGroupByKey creates Iterable, not list. #16099

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Merged
merged 3 commits into from
Dec 16, 2021
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Clarify CoGroupByKey creates Iterable, not list. #16099

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fa45751
Clarify CoGroupByKey creates Iterable, not list.
rainwoodman Dec 1, 2021
307567c
Update sdks/python/apache_beam/transforms/util.py
TheNeuralBit Dec 16, 2021
e709d39
Remove trailing whitespace
TheNeuralBit Dec 16, 2021
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16 changes: 11 additions & 5 deletions sdks/python/apache_beam/transforms/util.py
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Expand Up @@ -111,24 +111,28 @@ class CoGroupByKey(PTransform):
'tag2': ... ,
... })

where `[]` refers to an iterable, not a list.

For example, given::

{'tag1': pc1, 'tag2': pc2, 333: pc3}

where::

pc1 = [(k1, v1)]
pc2 = []
pc3 = [(k1, v31), (k1, v32), (k2, v33)]
pc1 = beam.Create([(k1, v1)]))
pc2 = beam.Create([])
pc3 = beam.Create([(k1, v31), (k1, v32), (k2, v33)])

The output PCollection would be::
The output PCollection would consist of items::

[(k1, {'tag1': [v1], 'tag2': [], 333: [v31, v32]}),
(k2, {'tag1': [], 'tag2': [], 333: [v33]})]

where `[]` refers to an iterable, not a list.

CoGroupByKey also works for tuples, lists, or other flat iterables of
PCollections, in which case the values of the resulting PCollections
will be tuples whose nth value is the list of values from the nth
will be tuples whose nth value is the iterable of values from the nth
PCollection---conceptually, the "tags" are the indices into the input.
Thus, for this input::

Expand All @@ -139,6 +143,8 @@ class CoGroupByKey(PTransform):
[(k1, ([v1], [], [v31, v32]),
(k2, ([], [], [v33]))]

where, again, `[]` refers to an iterable, not a list.

Attributes:
**kwargs: Accepts a single named argument "pipeline", which specifies the
pipeline that "owns" this PTransform. Ordinarily CoGroupByKey can obtain
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