Source code for abydos.distance._ncd_lzma

# Copyright 2014-2020 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,
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"""abydos.distance._ncd_lzma.

NCD using LZMA
"""

import lzma

from typing import Any

from ._distance import _Distance


__all__ = ['NCDlzma']


[docs] class NCDlzma(_Distance): """Normalized Compression Distance using LZMA compression. Cf. https://en.wikipedia.org/wiki/Lempel-Ziv-Markov_chain_algorithm Normalized compression distance (NCD) :cite:`Cilibrasi:2005`. .. versionadded:: 0.3.6 """ _level = 6 def __init__(self, level: int = 6, **kwargs: Any) -> None: """Initialize LZMA compressor. Parameters ---------- level : int The compression level (0 to 9) .. versionadded:: 0.5.0 """ super().__init__(**kwargs) self._level = level
[docs] def dist(self, src: str, tar: str) -> float: """Return the NCD between two strings using LZMA compression. Parameters ---------- src : str Source string for comparison tar : str Target string for comparison Returns ------- float Compression distance Examples -------- >>> cmp = NCDlzma() >>> cmp.dist('cat', 'hat') 0.08695652173913043 >>> cmp.dist('Niall', 'Neil') 0.16 >>> cmp.dist('aluminum', 'Catalan') 0.16 >>> cmp.dist('ATCG', 'TAGC') 0.08695652173913043 .. versionadded:: 0.3.5 .. versionchanged:: 0.3.6 Encapsulated in class """ if src == tar: return 0.0 src_b = src.encode('utf-8') tar_b = tar.encode('utf-8') src_comp = lzma.compress(src_b, preset=self._level)[14:] tar_comp = lzma.compress(tar_b, preset=self._level)[14:] concat_comp = lzma.compress(src_b + tar_b, preset=self._level)[14:] concat_comp2 = lzma.compress(tar_b + src_b, preset=self._level)[14:] 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()