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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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