我正在尝试从大型语料库中找到k个最常见的n-gram。我已经看到很多地方暗示了这种天真的方法 - 只需扫描整个语料库并保留所有n-gram数量的字典。有更好的方法吗?
答案 0 :(得分:3)
在Python中,使用NLTK:
$ wget http://norvig.com/big.txt
$ python
>>> from collections import Counter
>>> from nltk import ngrams
>>> bigtxt = open('big.txt').read()
>>> ngram_counts = Counter(ngrams(bigtxt.split(), 2))
>>> ngram_counts.most_common(10)
[(('of', 'the'), 12422), (('in', 'the'), 5741), (('to', 'the'), 4333), (('and', 'the'), 3065), (('on', 'the'), 2214), (('at', 'the'), 1915), (('by', 'the'), 1863), (('from', 'the'), 1754), (('of', 'a'), 1700), (('with', 'the'), 1656)]
在Python中,原生(参见Fast/Optimize N-gram implementations in python):
>>> def ngrams(text, n=2):
... return zip(*[text[i:] for i in range(n)])
>>> ngram_counts = Counter(ngrams(bigtxt.split(), 2))
>>> ngram_counts.most_common(10)
[(('of', 'the'), 12422), (('in', 'the'), 5741), (('to', 'the'), 4333), (('and', 'the'), 3065), (('on', 'the'), 2214), (('at', 'the'), 1915), (('by', 'the'), 1863), (('from', 'the'), 1754), (('of', 'a'), 1700), (('with', 'the'), 1656)]
在朱莉娅,请参阅Generate ngrams with Julia
import StatsBase: countmap
import Iterators: partition
bigtxt = readstring(open("big.txt"))
ngram_counts = countmap(collect(partition(split(bigtxt), 2, 1)))
粗略的时机:
$ time python ngram-test.py # With NLTK.
real 0m3.166s
user 0m2.274s
sys 0m0.528s
$ time python ngram-native-test.py
real 0m1.521s
user 0m1.317s
sys 0m0.145s
$ time julia ngram-test.jl
real 0m3.573s
user 0m3.188s
sys 0m0.306s