Source code for abydos.distance._doolittle

# Copyright 2018-2020 by Christopher C. Little.
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# Abydos is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
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Doolittle similarity

from ._token_distance import _TokenDistance

__all__ = ['Doolittle']

[docs]class Doolittle(_TokenDistance): r"""Doolittle similarity. For two sets X and Y and a population N, the Doolittle similarity :cite:`Doolittle:1884` is .. math:: sim_{Doolittle}(X, Y) = \frac{(|X \cap Y| \cdot |N| - |X| \cdot |Y|)^2} {|X| \cdot |Y| \cdot |N \setminus Y| \cdot |N \setminus X|} In :ref:`2x2 confusion table terms <confusion_table>`, where a+b+c+d=n, this is .. math:: sim_{Doolittle} = \frac{(an-(a+b)(a+c))^2}{(a+b)(a+c)(b+d)(c+d)} .. versionadded:: 0.4.0 """ def __init__( self, alphabet=None, tokenizer=None, intersection_type='crisp', **kwargs ): """Initialize Doolittle instance. Parameters ---------- alphabet : Counter, collection, int, or None This represents the alphabet of possible tokens. See :ref:`alphabet <alphabet>` description in :py:class:`_TokenDistance` for details. tokenizer : _Tokenizer A tokenizer instance from the :py:mod:`abydos.tokenizer` package intersection_type : str Specifies the intersection type, and set type as a result: See :ref:`intersection_type <intersection_type>` description in :py:class:`_TokenDistance` for details. **kwargs Arbitrary keyword arguments Other Parameters ---------------- qval : int The length of each q-gram. Using this parameter and tokenizer=None will cause the instance to use the QGram tokenizer with this q value. metric : _Distance A string distance measure class for use in the ``soft`` and ``fuzzy`` variants. threshold : float A threshold value, similarities above which are counted as members of the intersection for the ``fuzzy`` variant. .. versionadded:: 0.4.0 """ super(Doolittle, self).__init__( alphabet=alphabet, tokenizer=tokenizer, intersection_type=intersection_type, **kwargs )
[docs] def sim(self, src, tar): """Return the Doolittle similarity of two strings. Parameters ---------- src : str Source string (or QGrams/Counter objects) for comparison tar : str Target string (or QGrams/Counter objects) for comparison Returns ------- float Doolittle similarity Examples -------- >>> cmp = Doolittle() >>> cmp.sim('cat', 'hat') 0.24744247205785666 >>> cmp.sim('Niall', 'Neil') 0.13009912077202224 >>> cmp.sim('aluminum', 'Catalan') 0.011710186806836291 >>> cmp.sim('ATCG', 'TAGC') 4.1196952743799446e-05 .. versionadded:: 0.4.0 """ if src == tar: return 1.0 self._tokenize(src, tar) a = self._intersection_card() b = self._src_only_card() c = self._tar_only_card() d = self._total_complement_card() num = (a * d - b * c) ** 2 if num == 0.0: return 0.0 return num / ((a + b) * (a + c) * (b + d) * (c + d))
if __name__ == '__main__': import doctest doctest.testmod()