Converting a generator expression () to list?

Question

I'm doing some topic modeling and am looking to store some of the results of my analysis.

import pandas as pd, numpy as np, scipy
import sklearn.feature_extraction.text as text
from sklearn import decomposition

descs = ["You should not go there", "We may go home later", "Why should we do your chores", "What should we do"]

vectorizer = text.CountVectorizer()

dtm = vectorizer.fit_transform(descs).toarray()

vocab = np.array(vectorizer.get_feature_names())

nmf = decomposition.NMF(3, random_state = 1)

topic = nmf.fit_transform(dtm)

topic_words = []

for t in nmf.components_:
    word_idx = np.argsort(t)[::-1][:20]
    topic_words.append(vocab[i] for i in word_idx)

for t in range(len(topic_words)):
    print("Topic {}: {}\n".format(t, " ".join([word for word in topic_words[t]])))

Prints:

Topic 0: do we should your why chores what you there not may later home go

Topic 1: should you there not go what do we your why may later home chores

Topic 2: we may later home go what do should your you why there not chores

I'm trying to write those topics to a file, so I thought storing them in a list might work, like this:

l = []
for t in range(len(topic_words)):
    l.append([word for word in topic_words[t]])
    print("Topic {}: {}\n".format(t, " ".join([word for word in topic_words[t]])))

But l just ends up as an empty array. How can I store these words in a list?

An off-topic style note: never use `l` for a variable name, it looks too much like the number `1`. — Mark Ransom, Jul 22 '16 at 21:17

score 3 · Accepted Answer · answered Jul 22 '16 at 21:11

You're appending generator expressions to your list topic_words, so the first time you printed, the generator expressions are already exhausted. You can instead do:

topic_words = []

for t in nmf.components_:
    word_idx = np.argsort(t)[::-1][:20]
    topic_words.append([vocab[i] for i in word_idx])
#                      ^                          ^

With this, you apparently won't need a new list, and you can print out with:

for t, words in enumerate(topic_words, 1):
    print("Topic {}: {}\n".format(t, " ".join(words)))

Converting a generator expression () to list?

1 Answers1