# 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._rouge_s.
Rouge-S similarity
"""
from ._distance import _Distance
from ..tokenizer import QSkipgrams
from ..util._ncr import _ncr
__all__ = ['RougeS']
[docs]class RougeS(_Distance):
r"""Rouge-S similarity.
Rouge-S similarity :cite:`Lin:2004`, operating on character-level skipgrams
.. versionadded:: 0.4.0
"""
def __init__(self, qval=2, **kwargs):
"""Initialize RougeS instance.
Parameters
----------
**kwargs
Arbitrary keyword arguments
.. versionadded:: 0.4.0
"""
super(RougeS, self).__init__(**kwargs)
self._qval = qval
self._tokenizer = QSkipgrams(qval=qval, start_stop='')
[docs] def sim(self, src, tar, beta=8):
"""Return the Rouge-S similarity of two strings.
Parameters
----------
src : str
Source string for comparison
tar : str
Target string for comparison
beta : int or float
A weighting factor to prejudice similarity towards src
Returns
-------
float
Rouge-S similarity
Examples
--------
>>> cmp = RougeS()
>>> cmp.sim('cat', 'hat')
0.3333333333333333
>>> cmp.sim('Niall', 'Neil')
0.30185758513931893
>>> cmp.sim('aluminum', 'Catalan')
0.10755653612796467
>>> cmp.sim('ATCG', 'TAGC')
0.6666666666666666
.. versionadded:: 0.4.0
"""
if src == tar:
return 1.0
qsg_src = self._tokenizer.tokenize(src).get_counter()
qsg_tar = self._tokenizer.tokenize(tar).get_counter()
intersection = sum((qsg_src & qsg_tar).values())
if intersection:
r_skip = intersection / _ncr(len(src), self._qval)
p_skip = intersection / _ncr(len(tar), self._qval)
else:
return 0.0
beta_sq = beta * beta
return (1 + beta_sq) * r_skip * p_skip / (r_skip + beta_sq * p_skip)
if __name__ == '__main__':
import doctest
doctest.testmod()