# -*- coding: utf-8 -*-
# Copyright 2014-2018 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.qgram.
The qgram module defines the QGrams multi-set class
"""
from __future__ import division, unicode_literals
from collections import Counter, Iterable
from six.moves import range
__all__ = ['QGrams']
[docs]class QGrams(Counter):
"""A q-gram class, which functions like a bag/multiset.
A q-gram is here defined as all sequences of q characters. Q-grams are also
known as k-grams and n-grams, but the term n-gram more typically refers to
sequences of whitespace-delimited words in a string, where q-gram refers
to sequences of characters in a word or string.
"""
term = ''
term_ss = ''
ordered_list = []
def __init__(self, term, qval=2, start_stop='$#', skip=0):
"""Initialize QGrams.
:param str term: a string to extract q-grams from
:param int or iterable qval: the q-gram length (defaults to 2), can be
an integer, range object, or list
:param str start_stop: a string of length >= 0 indicating start & stop
symbols.
If the string is '', q-grams will be calculated without start &
stop symbols appended to each end.
Otherwise, the first character of start_stop will pad the beginning
of the string and the last character of start_stop will pad the end
of the string before q-grams are calculated. (In the case that
start_stop is only 1 character long, the same symbol will be used
for both.)
:param int or iterable skip: the number of characters to skip, can be
an integer, range object, or list
>>> qg = QGrams('AATTATAT')
>>> qg
QGrams({'AT': 3, 'TA': 2, '$A': 1, 'AA': 1, 'TT': 1, 'T#': 1})
>>> qg = QGrams('AATTATAT', qval=1, start_stop='')
>>> qg
QGrams({'A': 4, 'T': 4})
>>> qg = QGrams('AATTATAT', qval=3, start_stop='')
>>> qg
QGrams({'TAT': 2, 'AAT': 1, 'ATT': 1, 'TTA': 1, 'ATA': 1})
"""
# Save the term itself
self.term = term
self.ordered_list = []
if not isinstance(qval, Iterable):
qval = (qval,)
if not isinstance(skip, Iterable):
skip = (skip,)
for qval_i in qval:
for skip_i in skip:
if len(self.term) < qval_i or qval_i < 1:
continue
if start_stop and qval_i > 1:
term = (start_stop[0]*(qval_i-1) + self.term +
start_stop[-1]*(qval_i-1))
else:
term = self.term
# Having appended start & stop symbols (or not), save the
# result, but only for the longest valid qval_i
if len(term) > len(self.term_ss):
self.term_ss = term
skip_i += 1
self.ordered_list += [term[i:i+(qval_i*skip_i):skip_i] for i in
range(len(term)-(qval_i-1))]
super(QGrams, self).__init__(self.ordered_list)
[docs] def count(self):
"""Return q-grams count.
:returns: the total count of q-grams in a QGrams object
:rtype: int
>>> qg = QGrams('AATTATAT')
>>> qg.count()
9
>>> qg = QGrams('AATTATAT', qval=1, start_stop='')
>>> qg.count()
8
>>> qg = QGrams('AATTATAT', qval=3, start_stop='')
>>> qg.count()
6
"""
return sum(self.values())
if __name__ == '__main__':
import doctest
doctest.testmod()