# 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._ncd_lzss.
NCD using LZSS
"""
from ._distance import _Distance
try:
import lzss
except ImportError: # pragma: no cover
# If the system lacks the lzss library, that's fine, but LZSS compression
# similarity won't be supported.
lzss = None
__all__ = ['NCDlzss']
[docs]class NCDlzss(_Distance):
"""Normalized Compression Distance using LZSS compression.
Cf. https://en.wikipedia.org/wiki/Lempel-Ziv-Storer-Szymanski
Normalized compression distance (NCD) :cite:`Cilibrasi:2005`.
.. versionadded:: 0.4.0
"""
[docs] def dist(self, src, tar):
"""Return the NCD between two strings using LZSS compression.
Parameters
----------
src : str
Source string for comparison
tar : str
Target string for comparison
Returns
-------
float
Compression distance
Raises
------
ValueError
Install the PyLZSS module in order to use LZSS
Examples
--------
>>> cmp = NCDlzss()
>>> cmp.dist('cat', 'hat')
0.75
>>> cmp.dist('Niall', 'Neil')
1.0
>>> cmp.dist('aluminum', 'Catalan')
1.0
>>> cmp.dist('ATCG', 'TAGC')
0.8
.. versionadded:: 0.4.0
"""
if src == tar:
return 0.0
if lzss is not None:
src_comp = lzss.encode(src)
tar_comp = lzss.encode(tar)
concat_comp = lzss.encode(src + tar)
concat_comp2 = lzss.encode(tar + src)
else: # pragma: no cover
raise ValueError('Install the PyLZSS module in order to use LZSS')
return (
min(len(concat_comp), len(concat_comp2))
- min(len(src_comp), len(tar_comp))
) / max(len(src_comp), len(tar_comp))
if __name__ == '__main__':
import doctest
doctest.testmod()