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