How to find the lemmas and frequency count of each word in list of sentences in a list?

Question

I want to find out the lemmas using WordNet Lemmatizer and also I need to compute each word frequency.

I am getting the following error.

The trace is as follows:

TypeError: unhashable type: 'list'

Note: The corpus is available on the nltk package itself.

What I have tried so far is as follows:

import nltk, re
import string
from collections import Counter
from string import punctuation
from nltk.tokenize import TweetTokenizer, sent_tokenize, word_tokenize
from nltk.corpus import gutenberg, stopwords
from nltk.stem import WordNetLemmatizer

def remove_punctuation(from_text):
    table = str.maketrans('', '', string.punctuation)
    stripped = [w.translate(table) for w in from_text]
    return stripped

def preprocessing():
    raw_data = (gutenberg.raw('shakespeare-hamlet.txt'))
    tokens_sentences = sent_tokenize(raw_data)
    tokens = [[word.lower() for word in line.split()] for line in tokens_sentences]
    print(len(tokens))
    global stripped_tokens
    stripped_tokens = [remove_punctuation(i) for i in tokens]
    sw = (stopwords.words('english'))
    filter_set = [[token for token in sentence if (token.lower() not in sw and token.isalnum())] for sentence in stripped_tokens]
    lemma= WordNetLemmatizer()
    global lem
    lem = []
    for w in filter_set:
        lem.append(lemma.lemmatize(w))

preprocessing()

Please help me in resolving the issue.

Answer 1

The problem is that lemma.lemmatize expects a string and you are passing a list. The elements of filter_set are lists. You need to change the line:

lem.append(lemma.lemmatize(w))

to something like this:

lem.append([wi for wi in map(lemma.lemmatize, w)])

The above code applies lemma.lemmatize to each token (wi) in w. Full code:

import nltk, re
import string
from collections import Counter
from string import punctuation
from nltk.tokenize import TweetTokenizer, sent_tokenize, word_tokenize
from nltk.corpus import gutenberg, stopwords
from nltk.stem import WordNetLemmatizer


def remove_punctuation(from_text):
    table = str.maketrans('', '', string.punctuation)
    stripped = [w.translate(table) for w in from_text]
    return stripped


def preprocessing():
    raw_data = (gutenberg.raw('shakespeare-hamlet.txt'))
    tokens_sentences = sent_tokenize(raw_data)
    tokens = [[word.lower() for word in line.split()] for line in tokens_sentences]
    print(len(tokens))
    stripped_tokens = [remove_punctuation(i) for i in tokens]
    sw = (stopwords.words('english'))
    filter_set = [[token for token in sentence if (token.lower() not in sw and token.isalnum())] for sentence in
                  stripped_tokens]
    lemma = WordNetLemmatizer()
    lem = []
    for w in filter_set:
        lem.append([wi for wi in map(lemma.lemmatize, w)])

    return lem

result = preprocessing()
for e in result[:10]:  # take the first 10 results
    print(e)

Output

['tragedie', 'hamlet', 'william', 'shakespeare', '1599', 'actus', 'primus']
['scoena', 'prima']
['enter', 'barnardo', 'francisco', 'two', 'centinels']
['barnardo']
['who']
['fran']
['nay', 'answer', 'stand', 'vnfold', 'selfe', 'bar']
['long', 'liue', 'king', 'fran']
['barnardo']
['bar']

UPDATE

To get the frequencies you can use Counter:

result = preprocessing()
frequencies = Counter(word for sentence in result for word in sentence)
for word, frequency in frequencies.most_common(10):  # get the 10 most frequent words
    print(word, frequency)

Output

ham 337
lord 217
king 180
haue 175
come 127
let 107
shall 107
hamlet 107
thou 105
good 98