# Copyright 2019-2020 by Christopher C. Little.
# This file is part of Abydos.
#
# Abydos is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# Abydos is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with Abydos. If not, see <http://www.gnu.org/licenses/>.
"""abydos.distance._lig3.
LIG3 similarity
"""
from ._distance import _Distance
from ._levenshtein import Levenshtein
__all__ = ['LIG3']
[docs]class LIG3(_Distance):
r"""LIG3 similarity.
:cite:`Snae:2002` proposes three Levenshtein-ISG-Guth hybrid similarity
measures: LIG1, LIG2, and LIG3. Of these, LIG1 is identical to ISG and LIG2
is identical to normalized Levenshtein similarity. Only LIG3 is a novel
measure, defined as:
.. math::
sim_{LIG3}(X, Y) = \frac{2I}{2I+C}
Here, I is the number of exact matches between the two words, truncated to
the length of the shorter word, and C is the Levenshtein distance between
the two words.
.. versionadded:: 0.4.1
"""
_lev = Levenshtein()
[docs] def sim(self, src, tar):
"""Return the LIG3 similarity of two words.
Parameters
----------
src : str
Source string for comparison
tar : str
Target string for comparison
Returns
-------
float
The LIG3 similarity
Examples
--------
>>> cmp = LIG3()
>>> cmp.sim('cat', 'hat')
0.8
>>> cmp.sim('Niall', 'Neil')
0.5714285714285714
>>> cmp.sim('aluminum', 'Catalan')
0.0
>>> cmp.sim('ATCG', 'TAGC')
0.0
.. versionadded:: 0.4.1
"""
if src == tar:
return 1.0
matches = 2 * sum(
src[pos] == tar[pos] for pos in range(min(len(src), len(tar)))
)
cost = self._lev.dist_abs(src, tar)
return matches / (matches + cost)
if __name__ == '__main__':
import doctest
doctest.testmod()