TfIdfVectorizer: How does the vectorizer with fixed vocab deal with new words?

Question

I\'m working on a corpus of ~100k research papers. I\'m considering three fields:

1. plaintext
2. title
3. abstract

I used the TfIdfVec

Answer 1

I'm afraid the matrix might be too large. It would be 96582*96582=9328082724 cells. Try to slice titles_tfidf a bit and check.

Source: http://scipy-user.10969.n7.nabble.com/SciPy-User-strange-error-when-creating-csr-matrix-td20129.html

EDT: If you are using older SciPy/Numpy version you might want to update: https://github.com/scipy/scipy/pull/4678

EDT2: Also if you are using 32bit python, switching to 64bit might help (I suppose)

EDT3: Answering your original question. When you use vocabulary from plaintexts and there will be new words in titles they will be ignored - but not influence tfidf value. Hope this snippet may make it more understandable:

from sklearn.feature_extraction.text import TfidfVectorizer
from sklearn.metrics.pairwise import cosine_similarity

plaintexts =["They are", "plain texts texts amoersand here"]
titles = ["And here", "titles ", "wolf dog eagle", "But here plain"]

vectorizer = TfidfVectorizer()
plaintexts_tfidf = vectorizer.fit_transform(plaintexts)
vocab = vectorizer.vocabulary_
vectorizer = TfidfVectorizer(vocabulary=vocab)
titles_tfidf = vectorizer.fit_transform(titles)
print('values using vocabulary')
print(titles_tfidf)
print(vectorizer.get_feature_names())
print('Brand new vectorizer')
vectorizer = TfidfVectorizer()
titles_tfidf = vectorizer.fit_transform(titles)
print(titles_tfidf)
print(vectorizer.get_feature_names())

Result is:

values using vocabulary
  (0, 2)        1.0
  (3, 3)        0.78528827571
  (3, 2)        0.61913029649
['amoersand', 'are', 'here', 'plain', 'texts', 'they']
Brand new vectorizer
  (0, 0)        0.78528827571
  (0, 4)        0.61913029649
  (1, 6)        1.0
  (2, 7)        0.57735026919
  (2, 2)        0.57735026919
  (2, 3)        0.57735026919
  (3, 4)        0.486934264074
  (3, 1)        0.617614370976
  (3, 5)        0.617614370976
['and', 'but', 'dog', 'eagle', 'here', 'plain', 'titles', 'wolf']

Notice it is not the same as I would remove words that not occur in plaintexts from titles.