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copied!<p>Generalized to n-grams with optional padding, also uses <code>defaultdict(int)</code> for frequencies, to work in 2.6:</p> <pre><code>from collections import defaultdict def ngrams(words, n=2, padding=False): "Compute n-grams with optional padding" pad = [] if not padding else [None]*(n-1) grams = pad + words + pad return (tuple(grams[i:i+n]) for i in range(0, len(grams) - (n - 1))) # grab n-grams words = ['the','cat','sat','on','the','dog','on','the','cat'] for size, padding in ((3, 0), (4, 0), (2, 1)): print '\n%d-grams padding=%d' % (size, padding) print list(ngrams(words, size, padding)) # show frequency counts = defaultdict(int) for ng in ngrams(words, 2, False): counts[ng] += 1 print '\nfrequencies of bigrams:' for c, ng in sorted(((c, ng) for ng, c in counts.iteritems()), reverse=True): print c, ng </code></pre> <p>Output:</p> <pre><code>3-grams padding=0 [('the', 'cat', 'sat'), ('cat', 'sat', 'on'), ('sat', 'on', 'the'), ('on', 'the', 'dog'), ('the', 'dog', 'on'), ('dog', 'on', 'the'), ('on', 'the', 'cat')] 4-grams padding=0 [('the', 'cat', 'sat', 'on'), ('cat', 'sat', 'on', 'the'), ('sat', 'on', 'the', 'dog'), ('on', 'the', 'dog', 'on'), ('the', 'dog', 'on', 'the'), ('dog', 'on', 'the', 'cat')] 2-grams padding=1 [(None, 'the'), ('the', 'cat'), ('cat', 'sat'), ('sat', 'on'), ('on', 'the'), ('the', 'dog'), ('dog', 'on'), ('on', 'the'), ('the', 'cat'), ('cat', None)] frequencies of bigrams: 2 ('the', 'cat') 2 ('on', 'the') 1 ('the', 'dog') 1 ('sat', 'on') 1 ('dog', 'on') 1 ('cat', 'sat') </code></pre>

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