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# Copyright 2014-2020 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._ncd_lzma. |
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NCD using LZMA |
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""" |
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import lzma |
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from typing import Any |
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from ._distance import _Distance |
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__all__ = ['NCDlzma'] |
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class NCDlzma(_Distance): |
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"""Normalized Compression Distance using LZMA compression. |
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Cf. https://en.wikipedia.org/wiki/Lempel-Ziv-Markov_chain_algorithm |
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Normalized compression distance (NCD) :cite:`Cilibrasi:2005`. |
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.. versionadded:: 0.3.6 |
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""" |
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_level = 6 |
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def __init__(self, level: int = 6, **kwargs: Any) -> None: |
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"""Initialize LZMA compressor. |
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Parameters |
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---------- |
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level : int |
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The compression level (0 to 9) |
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.. versionadded:: 0.5.0 |
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""" |
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super().__init__(**kwargs) |
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self._level = level |
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def dist(self, src: str, tar: str) -> float: |
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"""Return the NCD between two strings using LZMA compression. |
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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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Returns |
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------- |
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float |
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Compression distance |
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Examples |
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-------- |
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>>> cmp = NCDlzma() |
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>>> cmp.dist('cat', 'hat') |
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0.08695652173913043 |
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>>> cmp.dist('Niall', 'Neil') |
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0.16 |
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>>> cmp.dist('aluminum', 'Catalan') |
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0.16 |
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>>> cmp.dist('ATCG', 'TAGC') |
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0.08695652173913043 |
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.. versionadded:: 0.3.5 |
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.. versionchanged:: 0.3.6 |
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Encapsulated in class |
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""" |
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if src == tar: |
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return 0.0 |
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src_b = src.encode('utf-8') |
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tar_b = tar.encode('utf-8') |
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src_comp = lzma.compress(src_b, preset=self._level)[14:] |
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tar_comp = lzma.compress(tar_b, preset=self._level)[14:] |
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concat_comp = lzma.compress(src_b + tar_b, preset=self._level)[14:] |
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concat_comp2 = lzma.compress(tar_b + src_b, preset=self._level)[14:] |
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return ( |
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min(len(concat_comp), len(concat_comp2)) |
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- min(len(src_comp), len(tar_comp)) |
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) / max(len(src_comp), len(tar_comp)) |
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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
