Confused with the return result of TfidfVectorizer.fit_transform

Question

I wanted to learn more about NLP. I came across this piece of code. But I was confused about the outcome of TfidfVectorizer.fit_transform when the result is printed. I am familiar with what tfidf is but I could not understand what the numbers mean.

import tensorflow as tf
import numpy as np
from sklearn.feature_extraction.text import TfidfVectorizer
import os
import io
import string
import requests
import csv
import nltk
from zipfile import ZipFile

sess = tf.Session()

batch_size = 100
max_features = 1000

save_file_name = os.path.join('smsspamcollection', 'SMSSpamCollection.csv')
if os.path.isfile(save_file_name):
    text_data = []
    with open(save_file_name, 'r') as temp_output_file:
        reader = csv.reader(temp_output_file)
        for row in reader:
            text_data.append(row)

else:
    zip_url = 'http://archive.ics.uci.edu/ml/machine-learning-databases/00228/smsspamcollection.zip'
    r = requests.get(zip_url)
    z = ZipFile(io.BytesIO(r.content))
    file = z.read('SMSSpamCollection')

    # Format data 
    text_data = file.decode()
    text_data = text_data.encode('ascii', errors='ignore')
    text_data = text_data.decode().split('\n')
    text_data = [x.split('\t') for x in text_data if len(x) >= 1]

    # And write to csv 
    with open(save_file_name, 'w') as temp_output_file:
        writer = csv.writer(temp_output_file)
        writer.writerows(text_data)

texts = [x[1] for x in text_data]
target = [x[0] for x in text_data]
target = [1 if x == 'spam' else 0 for x in target]

# Normalize the text
texts = [x.lower() for x in texts]  # lower
texts = [''.join(c for c in x if c not in string.punctuation) for x in texts]  # remove punctuation
texts = [''.join(c for c in x if c not in '0123456789') for x in texts]  # remove numbers
texts = [' '.join(x.split()) for x in texts]  # trim extra whitespace


def tokenizer(text):
    words = nltk.word_tokenize(text)
    return words


tfidf = TfidfVectorizer(tokenizer=tokenizer, stop_words='english', max_features=max_features)
sparse_tfidf_texts = tfidf.fit_transform(texts)
print(sparse_tfidf_texts)

And the output is:

(0, 630) 0.37172623140154337 (0, 160) 0.36805562944957004 (0, 38) 0.3613966215413548 (0, 545) 0.2561101665717327 (0, 326) 0.2645280991765623 (0, 967) 0.3277447602873963 (0, 421) 0.3896274380321477 (0, 227) 0.28102915589024796 (0, 323) 0.22032541100275282 (0, 922) 0.2709848154866997 (1, 577) 0.4007895093299793 (1, 425) 0.5970064521899725 (1, 943) 0.6310763941180291 (1, 878) 0.29102173465492637 (2, 282) 0.1771481430848552 (2, 243) 0.5517018054305785 (2, 955) 0.2920174942032025 (2, 138) 0.30143666813167863 (2, 946) 0.2269933441326121 (2, 165) 0.3051095293405041 (2, 268) 0.2820392223588522 (2, 780) 0.24119626642264894 (2, 823) 0.1890454397278538 (2, 674) 0.256251970757827 (2, 874) 0.19343834015314287 : : (5569, 648) 0.24171652492226922
(5569, 123) 0.23011909339432202 (5569, 957) 0.24817919217662862
(5569, 549) 0.28583789844730134 (5569, 863) 0.3026729783085827
(5569, 844) 0.20228305447951195 (5569, 146) 0.2514415602877767
(5569, 595) 0.2463259875380789 (5569, 511) 0.3091904754885042
(5569, 230) 0.2872728684768659 (5569, 638) 0.34151390143548765
(5569, 83) 0.3464271621701711 (5570, 370) 0.4199910200421362
(5570, 46) 0.48234172093857797 (5570, 317) 0.4171646676697801
(5570, 281) 0.6456993475093024 (5572, 282) 0.25540827228532487
(5572, 385) 0.36945842040023935 (5572, 448) 0.25540827228532487
(5572, 931) 0.3031800542518209 (5572, 192) 0.29866989620926737
(5572, 303) 0.43990016711221736 (5572, 87) 0.45211284173737176
(5572, 332) 0.3924202767503492 (5573, 866) 1.0

I would be more than happy if someone can explain about the output.

Answer 1

Note that you are printing a sparse matrix so the output looks different compared to printing a standard dense matrix. See below the main components:

• The tuple represents: (document_id, token_id)
• The value following the tuple represents the tf-idf score of a given token in a given document
• The tuples that are not there have a tf-idf score of 0

If you want to find what token the token_id corresponds to, check the get_feature_names method.