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48 lines
1.3 KiB
48 lines
1.3 KiB
6 years ago
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import itertools
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from .itertoolz import frequencies, pluck, getter
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from .compatibility import map
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__all__ = ('countby', 'partitionby')
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def countby(key, seq):
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""" Count elements of a collection by a key function
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>>> countby(len, ['cat', 'mouse', 'dog'])
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{3: 2, 5: 1}
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>>> def iseven(x): return x % 2 == 0
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>>> countby(iseven, [1, 2, 3]) # doctest:+SKIP
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{True: 1, False: 2}
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See Also:
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groupby
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"""
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if not callable(key):
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key = getter(key)
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return frequencies(map(key, seq))
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def partitionby(func, seq):
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""" Partition a sequence according to a function
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Partition `s` into a sequence of lists such that, when traversing
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`s`, every time the output of `func` changes a new list is started
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and that and subsequent items are collected into that list.
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>>> is_space = lambda c: c == " "
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>>> list(partitionby(is_space, "I have space"))
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[('I',), (' ',), ('h', 'a', 'v', 'e'), (' ',), ('s', 'p', 'a', 'c', 'e')]
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>>> is_large = lambda x: x > 10
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>>> list(partitionby(is_large, [1, 2, 1, 99, 88, 33, 99, -1, 5]))
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[(1, 2, 1), (99, 88, 33, 99), (-1, 5)]
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See also:
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partition
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groupby
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itertools.groupby
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"""
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return map(tuple, pluck(1, itertools.groupby(seq, key=func)))
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