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# -*- coding: utf-8 -*- |
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# Copyright 2014-2018 by Christopher C. Little. |
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# This file is part of Abydos. |
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# |
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# Abydos is free software: you can redistribute it and/or modify |
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# it under the terms of the GNU General Public License as published by |
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# the Free Software Foundation, either version 3 of the License, or |
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# (at your option) any later version. |
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# |
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# Abydos is distributed in the hope that it will be useful, |
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# but WITHOUT ANY WARRANTY; without even the implied warranty of |
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
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# GNU General Public License for more details. |
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# |
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# You should have received a copy of the GNU General Public License |
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# along with Abydos. If not, see <http://www.gnu.org/licenses/>. |
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"""abydos.distance._monge_elkan. |
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Monge-Elkan similarity & distance |
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""" |
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from __future__ import ( |
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absolute_import, |
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division, |
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print_function, |
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unicode_literals, |
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) |
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from ._distance import _Distance |
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from ._levenshtein import sim_levenshtein |
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from ..tokenizer import QGrams |
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__all__ = ['MongeElkan', 'dist_monge_elkan', 'sim_monge_elkan'] |
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class MongeElkan(_Distance): |
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"""Monge-Elkan similarity. |
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Monge-Elkan is defined in :cite:`Monge:1996`. |
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Note: Monge-Elkan is NOT a symmetric similarity algorithm. Thus, the |
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similarity of src to tar is not necessarily equal to the similarity of |
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tar to src. If the symmetric argument is True, a symmetric value is |
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calculated, at the cost of doubling the computation time (since |
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:math:`sim_{Monge-Elkan}(src, tar)` and :math:`sim_{Monge-Elkan}(tar, src)` |
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are both calculated and then averaged). |
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""" |
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def sim(self, src, tar, sim_func=sim_levenshtein, symmetric=False): |
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"""Return the Monge-Elkan similarity of two strings. |
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Parameters |
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---------- |
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src : str |
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Source string for comparison |
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tar : str |
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Target string for comparison |
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sim_func : function |
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The internal similarity metric to employ |
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symmetric : bool |
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Return a symmetric similarity measure |
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Returns |
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------- |
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float |
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Monge-Elkan similarity |
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Examples |
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-------- |
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>>> cmp = MongeElkan() |
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>>> cmp.sim('cat', 'hat') |
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0.75 |
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>>> round(cmp.sim('Niall', 'Neil'), 12) |
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0.666666666667 |
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>>> round(cmp.sim('aluminum', 'Catalan'), 12) |
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0.388888888889 |
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>>> cmp.sim('ATCG', 'TAGC') |
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0.5 |
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""" |
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if src == tar: |
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return 1.0 |
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q_src = sorted(QGrams(src).elements()) |
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q_tar = sorted(QGrams(tar).elements()) |
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if not q_src or not q_tar: |
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return 0.0 |
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sum_of_maxes = 0 |
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for q_s in q_src: |
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max_sim = float('-inf') |
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for q_t in q_tar: |
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max_sim = max(max_sim, sim_func(q_s, q_t)) |
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sum_of_maxes += max_sim |
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sim_em = sum_of_maxes / len(q_src) |
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if symmetric: |
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sim_em = (sim_em + self.sim(tar, src, sim_func, False)) / 2 |
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return sim_em |
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def sim_monge_elkan(src, tar, sim_func=sim_levenshtein, symmetric=False): |
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"""Return the Monge-Elkan similarity of two strings. |
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This is a wrapper for :py:meth:`MongeElkan.sim`. |
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Parameters |
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---------- |
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src : str |
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Source string for comparison |
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tar : str |
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Target string for comparison |
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sim_func : function |
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Rhe internal similarity metric to employ |
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symmetric : bool |
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Return a symmetric similarity measure |
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Returns |
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------- |
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float |
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Monge-Elkan similarity |
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Examples |
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-------- |
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>>> sim_monge_elkan('cat', 'hat') |
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0.75 |
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>>> round(sim_monge_elkan('Niall', 'Neil'), 12) |
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0.666666666667 |
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>>> round(sim_monge_elkan('aluminum', 'Catalan'), 12) |
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0.388888888889 |
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>>> sim_monge_elkan('ATCG', 'TAGC') |
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0.5 |
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""" |
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return MongeElkan().sim(src, tar, sim_func, symmetric) |
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def dist_monge_elkan(src, tar, sim_func=sim_levenshtein, symmetric=False): |
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"""Return the Monge-Elkan distance between two strings. |
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This is a wrapper for :py:meth:`MongeElkan.dist`. |
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Parameters |
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---------- |
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src : str |
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Source string for comparison |
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tar : str |
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Target string for comparison |
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sim_func : function |
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The internal similarity metric to employ |
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symmetric : bool |
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Return a symmetric similarity measure |
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Returns |
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------- |
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float |
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Monge-Elkan distance |
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Examples |
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-------- |
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>>> dist_monge_elkan('cat', 'hat') |
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0.25 |
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>>> round(dist_monge_elkan('Niall', 'Neil'), 12) |
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0.333333333333 |
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>>> round(dist_monge_elkan('aluminum', 'Catalan'), 12) |
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0.611111111111 |
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>>> dist_monge_elkan('ATCG', 'TAGC') |
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0.5 |
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""" |
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return MongeElkan().dist(src, tar, sim_func, symmetric) |
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if __name__ == '__main__': |
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import doctest |
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doctest.testmod() |
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chrislit /
abydos
