# 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._block_levenshtein.
Levenshtein distance with block operations
"""
from ._lcsstr import LCSstr
from ._levenshtein import Levenshtein
__all__ = ['BlockLevenshtein']
[docs]class BlockLevenshtein(Levenshtein):
"""Levenshtein distance with block operations.
In addition to character-level insert, delete, and replace operations,
this version of the Levenshtein distance supports block-level insert,
delete, and replace, provided that the block occurs in both input
strings.
.. versionadded:: 0.4.0
"""
def __init__(self, cost=(1, 1, 1, 1), normalizer=max, **kwargs):
"""Initialize BlockLevenshtein instance.
Parameters
----------
**kwargs
Arbitrary keyword arguments
.. versionadded:: 0.4.0
"""
super(BlockLevenshtein, self).__init__(
cost=cost, normalizer=normalizer, **kwargs
)
self.lcs = LCSstr()
[docs] def dist_abs(self, src, tar):
"""Return the block Levenshtein edit distance between two strings.
Parameters
----------
src : str
Source string for comparison
tar : str
Target string for comparison
Returns
-------
int
The block Levenshtein edit distance between src & tar
Examples
--------
>>> cmp = BlockLevenshtein()
>>> cmp.dist_abs('cat', 'hat')
1
>>> cmp.dist_abs('Niall', 'Neil')
3
>>> cmp.dist_abs('aluminum', 'Catalan')
7
>>> cmp.dist_abs('ATCG', 'TAGC')
3
.. versionadded:: 0.4.0
"""
alphabet = set(src) | set(tar)
next_char = ord('A')
lcs = self.lcs.lcsstr(src, tar)
while len(lcs) > 1:
while chr(next_char) in alphabet:
next_char += 1
p = self.lcs.lcsstr(src, tar)
src = src.replace(p, chr(next_char))
tar = tar.replace(p, chr(next_char))
alphabet.add(chr(next_char))
lcs = self.lcs.lcsstr(src, tar)
d = super(BlockLevenshtein, self).dist_abs(src, tar)
return d
[docs] def dist(self, src, tar):
"""Return the normalized block Levenshtein distance between strings.
Parameters
----------
src : str
Source string for comparison
tar : str
Target string for comparison
Returns
-------
float
The normalized Levenshtein distance with blocks between src & tar
Examples
--------
>>> cmp = BlockLevenshtein()
>>> round(cmp.dist('cat', 'hat'), 12)
0.333333333333
>>> round(cmp.dist('Niall', 'Neil'), 12)
0.6
>>> cmp.dist('aluminum', 'Catalan')
0.875
>>> cmp.dist('ATCG', 'TAGC')
0.75
.. versionadded:: 0.4.0
"""
if src == tar:
return 0.0
ins_cost, del_cost = self._cost[:2]
return self.dist_abs(src, tar) / (
self._normalizer([len(src) * del_cost, len(tar) * ins_cost])
)
if __name__ == '__main__':
import doctest
doctest.testmod()