I am using nltk
to generate n-grams from sentences by first removing given stop words. However, nltk.pos_tag()
is extremely slow taking up to 0.6 sec on my CPU (Intel i7).
The output:
['The first time I went, and was completely taken by the live jazz band and atmosphere, I ordered the Lobster Cobb Salad.']
0.620481014252
["It's simply the best meal in NYC."]
0.640982151031
['You cannot go wrong at the Red Eye Grill.']
0.644664049149
The code:
for sentence in source:
nltk_ngrams = None
if stop_words is not None:
start = time.time()
sentence_pos = nltk.pos_tag(word_tokenize(sentence))
print time.time() - start
filtered_words = [word for (word, pos) in sentence_pos if pos not in stop_words]
else:
filtered_words = ngrams(sentence.split(), n)
Is this really that slow or am I doing something wrong here?
The main problem with POS tagging is ambiguity. In English, many common words have multiple meanings and therefore multiple POS . The job of a POS tagger is to resolve this ambiguity accurately based on the context of use. For example, the word "shot" can be a noun or a verb.
POS tags make it possible for automatic text processing tools to take into account which part of speech each word is. This facilitates the use of linguistic criteria in addition to statistics.
The POS tagging process is the process of finding the sequence of tags which is most likely to have generated a given word sequence. We can model this POS process by using a Hidden Markov Model (HMM), where tags are the hidden states that produced the observable output, i.e., the words.
It is a process of converting a sentence to forms – list of words, list of tuples (where each tuple is having a form (word, tag)). The tag in case of is a part-of-speech tag, and signifies whether the word is a noun, adjective, verb, and so on. Default tagging is a basic step for the part-of-speech tagging.
Use pos_tag_sents
for tagging multiple sentences:
>>> import time
>>> from nltk.corpus import brown
>>> from nltk import pos_tag
>>> from nltk import pos_tag_sents
>>> sents = brown.sents()[:10]
>>> start = time.time(); pos_tag(sents[0]); print time.time() - start
0.934092998505
>>> start = time.time(); [pos_tag(s) for s in sents]; print time.time() - start
9.5061340332
>>> start = time.time(); pos_tag_sents(sents); print time.time() - start
0.939551115036
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