7

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.

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BBSysDyn
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5 Answers5

5

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']]
Markus Jarderot
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  • Finding the groups would be the hard part. I guess I could use a clustering algorithm that takes e.g. levenshtein distance as distance measure. After clusters are identified I pick one of the words (any of them) as representative for that group. – BBSysDyn Jul 18 '12 at 06:47
  • Alternatively, you can use the mean pairwise Levenshtein distance between the words in two groups as the distance measure between them (many hierarchical clustering algorithms work this way). The max pairwise distance might also work. – David Robinson Jul 18 '12 at 06:57
  • Lovely explanation of representative of group. However, I would recommend (double) metaphone over soundex. +1 – Jon Clements Jul 18 '12 at 07:11
  • Markus, could you add the mainline to the script above? I added a distance measure to your code (will be added to my main question), I had problems displaying the groups. – BBSysDyn Jul 18 '12 at 10:08
3

You have to decide in closed matches words, which words you want to use. May be get the first element from the list which get_close_matches is returning, or just use random function on that list and get one element from closed matches.

There must be some sort of rule, for it..

In [19]: import difflib

In [20]: a = ['ape', 'appel', 'apple', 'peach', 'puppy']

In [21]: a = ['appel', 'apple', 'peach', 'puppy']

In [22]: b = difflib.get_close_matches('ape',a)

In [23]: b
Out[23]: ['apple', 'appel']

In [24]: import random

In [25]: c = random.choice(b)

In [26]: c
Out[26]: 'apple'

In [27]:

Now remove c from the initial list, thats it... For c++, you can use Levenshtein_distance

Anton
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NIlesh Sharma
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3

Here is another version using Affinity Propagation algorithm. 

import numpy as np
import scipy.linalg as lin
import Levenshtein as leven
import matplotlib.pyplot as plt
from sklearn.cluster import KMeans
from sklearn.cluster import AffinityPropagation
import itertools

words = np.array(
    ['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'])

print "calculating distances..."

(dim,) = words.shape

f = lambda (x,y): -leven.distance(x,y)

res=np.fromiter(itertools.imap(f, itertools.product(words, words)), dtype=np.uint8)
A = np.reshape(res,(dim,dim))

af = AffinityPropagation().fit(A)
cluster_centers_indices = af.cluster_centers_indices_
labels = af.labels_

unique_labels = set(labels)
for i in unique_labels:
    print words[labels==i]

Distances had to be converted to similarities, I did that by taking the negative of distance. The output is

['to' 'you' 'do' 'by' 'so' 'who' 'go' 'into' 'also' 'two']
['it' 'with' 'at' 'if' 'get' 'its' 'first']
['of' 'for' 'from' 'or' 'your' 'look' 'after' 'work']
['the' 'be' 'have' 'I' 'he' 'we' 'her' 'she' 'me' 'give']
['this' 'his' 'which' 'him']
['and' 'a' 'in' 'an' 'my' 'all' 'can' 'any']
['on' 'one' 'good' 'some' 'see' 'only' 'come' 'over']
['would' 'could']
['but' 'out' 'about' 'our' 'most']
['make' 'like' 'time' 'take' 'back']
['that' 'they' 'there' 'their' 'when' 'them' 'other' 'than' 'then' 'think'
 'even' 'these']
['not' 'no' 'know' 'now' 'how' 'new']
['will' 'people' 'year' 'well']
['say' 'what' 'way' 'want' 'day']
['because']
['as' 'up' 'just' 'use' 'us']
BBSysDyn
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  • first let say thanks you save me for longs days of research ! I've added an improvement in your code instead of using the default euclidian distance in the affinitty propagation algorithm i change it to : precomputed so I change the line in this af = AffinityPropagation(affinity='precomputed').fit(A) and get better results than with the default. – Espoir Murhabazi Jun 23 '17 at 08:40
1

Another method could be using matrix factorization, using SVD. First we create word distance matrix, for 100 words this would be 100 x 100 matrix representating the distance from each word to all other words. Then, SVD is ran on this matrix, the u in the resulting u,s,v can be seen as membership strength to each cluster.

Code

import numpy as np
import scipy.linalg as lin
import Levenshtein as leven
import matplotlib.pyplot as plt
from sklearn.cluster import KMeans
import itertools

words = np.array(
    ['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'])

print "calculating distances..."

(dim,) = words.shape

f = lambda (x,y): leven.distance(x,y)
res=np.fromiter(itertools.imap(f, itertools.product(words, words)),
                dtype=np.uint8)
A = np.reshape(res,(dim,dim))

print "svd..."

u,s,v = lin.svd(A, full_matrices=False)

print u.shape
print s.shape
print s
print v.shape

data = u[:,0:10]
k=KMeans(init='k-means++', k=25, n_init=10)
k.fit(data)
centroids = k.cluster_centers_
labels = k.labels_
print labels

for i in range(np.max(labels)):
    print words[labels==i]

def dist(x,y):   
    return np.sqrt(np.sum((x-y)**2, axis=1))

print "centroid points.."
for i,c in enumerate(centroids):
    idx = np.argmin(dist(c,data[labels==i]))
    print words[labels==i][idx]
    print words[labels==i]

plt.plot(centroids[:,0],centroids[:,1],'x')
plt.hold(True)
plt.plot(u[:,0], u[:,1], '.')
plt.show()

from mpl_toolkits.mplot3d import Axes3D
fig = plt.figure()
ax = Axes3D(fig)
ax.plot(u[:,0], u[:,1], u[:,2],'.', zs=0,
        zdir='z', label='zs=0, zdir=z')
plt.show()

The result

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

The selection of k for number of clusters is important, k=25 gives much better results than k=20 for instance.

The code also selects a representative word for each cluster by picking the word whose u[..] coordinate is closest to the cluster centroid.

BBSysDyn
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0

Here is an approach based on medoids. First install MlPy. On Ubuntu

sudo apt-get install python-mlpy

Then

import numpy as np
import mlpy

class distance:    
    def compute(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]

x =  np.array(['ape', 'appel', 'apple', 'peach', 'puppy'])

km = mlpy.Kmedoids(k=3, dist=distance())
medoids,clusters,a,b = km.compute(x)

print medoids
print clusters
print a

print x[medoids] 
for i,c in enumerate(x[medoids]):
    print "medoid", c
    print x[clusters[a==i]]

The output is

[4 3 1]
[0 2]
[2 2]
['puppy' 'peach' 'appel']
medoid puppy
[]
medoid peach
[]
medoid appel
['ape' 'apple']

The bigger word list and using k=10

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