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32 lines
1.1 KiB
32 lines
1.1 KiB
"""
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Simple class which, given a sample, can quickly count the size of overlap with an iterable.
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All elements of sample must be hashable.
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This is mainly in its own file in order to be able to test and time possible alternative
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implementations.
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"""
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class MatchCounter(object):
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def __init__(self, sample):
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self.sample = set(sample)
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def count_unique(self, iterable):
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"""
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Returns the count of unique elements of iterable that are present in sample. The sample may
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only contain hashable elements, so non-hashable elements of iterable are never counted.
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"""
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# The simplest implementation is 5 times faster:
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# len(self.sample.intersection(iterable))
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# but fails if iterable can ever contain non-hashable values (e.g. list). This is the next
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# best alternative. Attempting to skip non-hashable values with `isinstance(v, Hashable)` is
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# another order of magnitude slower.
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seen = set()
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for v in iterable:
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try:
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if v in self.sample:
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seen.add(v)
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except TypeError:
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# Non-hashable values can't possibly be in self.sample, so just don't count those.
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pass
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return len(seen)
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