# 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._whittaker.
Whittaker distance
"""
from ._token_distance import _TokenDistance
__all__ = ['Whittaker']
[docs]class Whittaker(_TokenDistance):
r"""Whittaker distance.
For two multisets X and Y drawn from an alphabet S, Whittaker distance
:cite:`Whittaker:1952` is
.. math::
sim_{Whittaker}(X, Y) = 1 -
\frac{1}{2}\sum_{i \in S} \Bigg| \frac{|X_i|}{|X|} -
\frac{|Y_i|}{|Y|} \Bigg|
.. versionadded:: 0.4.0
"""
def __init__(self, tokenizer=None, **kwargs):
"""Initialize Whittaker instance.
Parameters
----------
tokenizer : _Tokenizer
A tokenizer instance from the :py:mod:`abydos.tokenizer` package
**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.
.. versionadded:: 0.4.0
"""
super(Whittaker, self).__init__(tokenizer=tokenizer, **kwargs)
[docs] def sim(self, src, tar):
"""Return the Whittaker distance of two strings.
Parameters
----------
src : str
Source string (or QGrams/Counter objects) for comparison
tar : str
Target string (or QGrams/Counter objects) for comparison
Returns
-------
float
Whittaker distance
Examples
--------
>>> cmp = Whittaker()
>>> cmp.sim('cat', 'hat')
0.5
>>> cmp.sim('Niall', 'Neil')
0.33333333333333
>>> cmp.sim('aluminum', 'Catalan')
0.11111111111111
>>> cmp.sim('ATCG', 'TAGC')
0.0
.. versionadded:: 0.4.0
"""
self._tokenize(src, tar)
alphabet = self._total().keys()
src_card = self._src_card()
tar_card = self._tar_card()
return float(
round(
1
- 0.5
* sum(
abs(
(self._src_tokens[tok] / src_card if src_card else 0.0)
- (
self._tar_tokens[tok] / tar_card
if tar_card
else 0.0
)
)
for tok in alphabet
),
14,
)
)
if __name__ == '__main__':
import doctest
doctest.testmod()