Question

this question is asked here before

What is a good strategy to group similar words?

but no clear answer is given on how to “group” items. The solution based on difflib is basically search, for given item, difflib can return the most similar word out of a list. But how can this be used for grouping?

I would like to reduce

['ape', 'appel', 'apple', 'peach', 'puppy']

to

['ape', 'appel', 'peach', 'puppy']

or

['ape', 'apple', 'peach', 'puppy']

One idea I tried was, for each item, iterate through the list, if get_close_matches returns more than one match, use it, if not keep the word as is. This partly worked, but it can suggest apple for appel, then appel for apple, these words would simply switch places and nothing would change.

I would appreciate any pointers, names of libraries, etc.

Note: also in terms of performance, we have a list of 300,000 items, and get_close_matches seems a bit slow. Does anyone know of a C/++ based solution out there?

Thanks,

Note: Further investigation revealed kmedoid is the right algorithm (as well as hierarchical clustering), since kmedoid does not require “centers”, it takes / uses data points themselves as centers (these points are called medoids, hence the name). In word grouping case, the medoid would be the representative element of that group / cluster.

Answer 1

You need to normalize the groups. In each group, pick one word or coding that represents the group. Then group the words by their representative.

Some possible ways:

• Pick the first encountered word.
• Pick the lexicographic first word.
• Derive a pattern for all the words.
• Pick an unique index.
• Use the soundex as pattern.

Grouping the words could be difficult, though. If A is similar to B, and B is similar to C, A and C is not necessarily similar to each other. If B is the representative, both A and C could be included in the group. But if A or C is the representative, the other could not be included.

---

Going by the first alternative (first encountered word):

class Seeder:
    def __init__(self):
        self.seeds = set()
        self.cache = dict()

    def get_seed(self, word):
        LIMIT = 2
        seed = self.cache.get(word,None)
        if seed is not None:
            return seed
        for seed in self.seeds:
            if self.distance(seed, word) <= LIMIT:
                self.cache[word] = seed
                return seed
        self.seeds.add(word)
        self.cache[word] = word
        return word

    def distance(self, s1, s2):
        l1 = len(s1)
        l2 = len(s2)
        matrix = [range(zz,zz + l1 + 1) for zz in xrange(l2 + 1)]
        for zz in xrange(0,l2):
            for sz in xrange(0,l1):
                if s1[sz] == s2[zz]:
                    matrix[zz+1][sz+1] = min(matrix[zz+1][sz] + 1, matrix[zz][sz+1] + 1, matrix[zz][sz])
                else:
                    matrix[zz+1][sz+1] = min(matrix[zz+1][sz] + 1, matrix[zz][sz+1] + 1, matrix[zz][sz] + 1)
        return matrix[l2][l1]

import itertools

def group_similar(words):
    seeder = Seeder()
    words = sorted(words, key=seeder.get_seed)
    groups = itertools.groupby(words, key=seeder.get_seed)
    return [list(v) for k,v in groups]

Example:

import pprint

print pprint.pprint(group_similar([
    'the', 'be', 'to', 'of', 'and', 'a', 'in', 'that', 'have',
    'I', 'it', 'for', 'not', 'on', 'with', 'he', 'as', 'you',
    'do', 'at', 'this', 'but', 'his', 'by', 'from', 'they', 'we',
    'say', 'her', 'she', 'or', 'an', 'will', 'my', 'one', 'all',
    'would', 'there', 'their', 'what', 'so', 'up', 'out', 'if',
    'about', 'who', 'get', 'which', 'go', 'me', 'when', 'make',
    'can', 'like', 'time', 'no', 'just', 'him', 'know', 'take',
    'people', 'into', 'year', 'your', 'good', 'some', 'could',
    'them', 'see', 'other', 'than', 'then', 'now', 'look',
    'only', 'come', 'its', 'over', 'think', 'also', 'back',
    'after', 'use', 'two', 'how', 'our', 'work', 'first', 'well',
    'way', 'even', 'new', 'want', 'because', 'any', 'these',
    'give', 'day', 'most', 'us'
]), width=120)

Output:

[['after'],
 ['also'],
 ['and', 'a', 'in', 'on', 'as', 'at', 'an', 'one', 'all', 'can', 'no', 'want', 'any'],
 ['back'],
 ['because'],
 ['but', 'about', 'get', 'just'],
 ['first'],
 ['from'],
 ['good', 'look'],
 ['have', 'make', 'give'],
 ['his', 'her', 'if', 'him', 'its', 'how', 'us'],
 ['into'],
 ['know', 'new'],
 ['like', 'time', 'take'],
 ['most'],
 ['of', 'I', 'it', 'for', 'not', 'he', 'you', 'do', 'by', 'we', 'or', 'my', 'so', 'up', 'out', 'go', 'me', 'now'],
 ['only'],
 ['over', 'our', 'even'],
 ['people'],
 ['say', 'she', 'way', 'day'],
 ['some', 'see', 'come'],
 ['the', 'be', 'to', 'that', 'this', 'they', 'there', 'their', 'them', 'other', 'then', 'use', 'two', 'these'],
 ['think'],
 ['well'],
 ['what', 'who', 'when', 'than'],
 ['with', 'will', 'which'],
 ['work'],
 ['would', 'could'],
 ['year', 'your']]