abydos/distance/_bag.py
# 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,
# 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._bag.
Bag similarity & distance
"""
from typing import Any, Optional
from ._token_distance import _TokenDistance
from ..tokenizer import CharacterTokenizer, _Tokenizer
__all__ = ['Bag']
class Bag(_TokenDistance):
"""Bag distance.
Bag distance is proposed in :cite:`Bartolini:2002`. It is defined as
.. math::
dist_{bag}(src, tar) =
max(|multiset(src)-multiset(tar)|, |multiset(tar)-multiset(src)|)
.. versionadded:: 0.3.6
"""
def __init__(
self,
tokenizer: Optional[_Tokenizer] = None,
intersection_type: str = 'crisp',
**kwargs: Any
) -> None:
"""Initialize Bag instance.
Parameters
----------
tokenizer : _Tokenizer
A tokenizer instance from the :py:mod:`abydos.tokenizer` package
intersection_type : str
Specifies the intersection type, and set type as a result:
See :ref:`intersection_type <intersection_type>` description in
:py:class:`_TokenDistance` for details.
**kwargs
Arbitrary keyword arguments
Other Parameters
----------------
qval : int
The length of each q-gram. Using this parameter and tokenizer=None
will cause the instance to use the QGram tokenizer with this
q value.
metric : _Distance
A string distance measure class for use in the ``soft`` and
``fuzzy`` variants.
threshold : float
A threshold value, similarities above which are counted as
members of the intersection for the ``fuzzy`` variant.
.. versionadded:: 0.4.0
"""
if tokenizer is None:
tokenizer = CharacterTokenizer()
super(Bag, self).__init__(
tokenizer=tokenizer, intersection_type=intersection_type, **kwargs
)
def dist_abs(self, src: str, tar: str, normalized: bool = False) -> float:
"""Return the bag distance between two strings.
Parameters
----------
src : str
Source string for comparison
tar : str
Target string for comparison
normalized : bool
Normalizes to [0, 1] if True
Returns
-------
int or float
Bag distance
Examples
--------
>>> cmp = Bag()
>>> cmp.dist_abs('cat', 'hat')
1
>>> cmp.dist_abs('Niall', 'Neil')
2
>>> cmp.dist_abs('aluminum', 'Catalan')
5
>>> cmp.dist_abs('ATCG', 'TAGC')
0
>>> cmp.dist_abs('abcdefg', 'hijklm')
7
>>> cmp.dist_abs('abcdefg', 'hijklmno')
8
.. versionadded:: 0.1.0
.. versionchanged:: 0.3.6
Encapsulated in class
"""
if tar == src:
return 0
elif not src:
return len(tar)
elif not tar:
return len(src)
self._tokenize(src, tar)
dist = max(self._src_only_card(), self._tar_only_card())
if normalized:
dist /= max(self._src_card(), self._tar_card())
return dist
def dist(self, src: str, tar: str) -> float:
"""Return the normalized bag distance between two strings.
Bag distance is normalized by dividing by :math:`max( |src|, |tar| )`.
Parameters
----------
src : str
Source string for comparison
tar : str
Target string for comparison
Returns
-------
float
Normalized bag distance
Examples
--------
>>> cmp = Bag()
>>> cmp.dist('cat', 'hat')
0.3333333333333333
>>> cmp.dist('Niall', 'Neil')
0.4
>>> cmp.dist('aluminum', 'Catalan')
0.625
>>> cmp.dist('ATCG', 'TAGC')
0.0
.. versionadded:: 0.1.0
.. versionchanged:: 0.3.6
Encapsulated in class
"""
if tar == src:
return 0.0
if not src or not tar:
return 1.0
return self.dist_abs(src, tar, normalized=True)
if __name__ == '__main__':
import doctest
doctest.testmod()