word2vec implementation with Python (& Gensim)

• Note: This code is written in Python 3.6.1 (+Gensim 2.3.0)

• Python implementation and application of word2vec with Gensim
  

import re
import numpy as np

from gensim.models import Word2Vec
from nltk.corpus import gutenberg
from multiprocessing import Pool
from scipy import spatial

• Import training dataset
• Import Shakespeare's Hamlet corpus from nltk library

sentences = list(gutenberg.sents('shakespeare-hamlet.txt'))   # import the corpus and convert into a list

print('Type of corpus: ', type(sentences))
print('Length of corpus: ', len(sentences))

Type of corpus: class 'list'
Length of corpus: 3106

print(sentences[0])    # title, author, and year
print(sentences[1])
print(sentences[10])

['[', 'The', 'Tragedie', 'of', 'Hamlet', 'by', 'William', 'Shakespeare', '1599', ']']
['Actus', 'Primus', '.']
['Fran', '.']

Preprocess data

• Use re module to preprocess data
• Convert all letters into lowercase
• Remove punctuations, numbers, etc.

for i in range(len(sentences)):
    sentences[i] = [word.lower() for word in sentences[i] if re.match('^[a-zA-Z]+', word)]  
print(sentences[0])    # title, author, and year
print(sentences[1])
print(sentences[10])

['the', 'tragedie', 'of', 'hamlet', 'by', 'william', 'shakespeare']
['actus', 'primus']
['fran']

Create and train model

• Create a word2vec model and train it with Hamlet corpus
• Key parameter description (https://radimrehurek.com/gensim/models/word2vec.html)
  • sentences: training data (has to be a list with tokenized sentences)
  • size: dimension of embedding space
  • sg: CBOW if 0, skip-gram if 1
  • window: number of words accounted for each context (if the window
  • size is 3, 3 word in the left neighorhood and 3 word in the right neighborhood are considered)
  • min_count: minimum count of words to be included in the vocabulary
  • iter: number of training iterations
  • workers: number of worker threads to train

model = Word2Vec(sentences = sentences, size = 100, sg = 1, window = 3, min_count = 1, iter = 10, workers = Pool()._processes)

model.init_sims(replace = True)

Save and load model

• word2vec model can be saved and loaded locally
• Doing so can reduce time to train model again

model.save('word2vec_model')
model = Word2Vec.load('word2vec_model')

Similarity calculation

• Similarity between embedded words (i.e., vectors) can be computed using metrics such as cosine similarity

model.most_similar('hamlet')

[('horatio', 0.9978846311569214),
('queene', 0.9971947073936462),
('laertes', 0.9971820116043091),
('king', 0.9968599081039429),
('mother', 0.9966716170310974),
('where', 0.9966292381286621),
('deere', 0.9965540170669556),
('ophelia', 0.9964221715927124),
('very', 0.9963752627372742),
('oh', 0.9963476657867432)]

v1 = model['king']
v2 = model['queen']

# define a function that computes cosine similarity between two words
def cosine_similarity(v1, v2):
    return 1 - spatial.distance.cosine(v1, v2)

cosine_similarity(v1, v2)

0.99437165260314941

References:

• Original paper: Mikolov, T., Chen, K., Corrado, G., & Dean, J. (2013). Efficient estimation of word representations in vector space. arXiv preprint arXiv:1301.3781.