Deep Inverse Regression with Yelp reviews

In this note we'll use gensim to turn the Word2Vec machinery into a document classifier, as in Document Classification by Inversion of Distributed Language Representations from ACL 2015.

Data and prep

First, download to the same directory as this note the data from the Yelp recruiting contest on kaggle:

You'll need to sign-up for kaggle.

You can then unpack the data and grab the information we need.

Tutorial Requirements:

  1. gensim (and all of its own requirements)
  2. pandas
  3. matplotlib
In [1]:
# ### uncomment below if you want...
# ## ... copious amounts of logging info
# import logging
# logging.basicConfig(format='%(asctime)s : %(levelname)s : %(message)s', level=logging.INFO)
# rootLogger = logging.getLogger()
# rootLogger.setLevel(logging.INFO)
# ## ... or auto-reload of gensim during development
# %load_ext autoreload
# %autoreload 2

First, we define a super simple parser

In [2]:
import re

contractions = re.compile(r"'|-|\"")
# all non alphanumeric
symbols = re.compile(r'(\W+)', re.U)
# single character removal
singles = re.compile(r'(\s\S\s)', re.I|re.U)
# separators (any whitespace)
seps = re.compile(r'\s+')

# cleaner (order matters)
def clean(text): 
    text = text.lower()
    text = contractions.sub('', text)
    text = symbols.sub(r' \1 ', text)
    text = singles.sub(' ', text)
    text = seps.sub(' ', text)
    return text

# sentence splitter
alteos = re.compile(r'([!\?])')
def sentences(l):
    l = alteos.sub(r' \1 .', l).rstrip("(\.)*\n")
    return l.split(".")

And put everything together in a review generator that provides tokenized sentences and the number of stars for every review.

In [3]:
from zipfile import ZipFile
import json

def YelpReviews(label):
    with ZipFile(""%label, 'r') as zf:
        with"yelp_%s_set/yelp_%s_set_review.json"%(label,label)) as f:
            for line in f:
                if type(line) is bytes:
                    line = line.decode('utf-8')
                rev = json.loads(line)
                yield {'y':rev['stars'],\
                       'x':[clean(s).split() for s in sentences(rev['text'])]}

For example:

In [4]:
except FileNotFoundError:
    raise ValueError("SKIP: Please download the")
{'x': [['nice', 'place', 'big', 'patio'],
  ['now', 'offering', 'live', 'sketch', 'comedy'],
  ['lighter', 'snappier', 'take', 'on', 'the', 'holiday', 'times'],
  ['not', 'for', 'the', 'easily', 'offended'],
  ['as', 'well', 'as', 'the', 'infectious', 'song', 'mama', 'christmas']],
 'y': 5}

Now, since the files are small we'll just read everything into in-memory lists. It takes a minute ...

In [5]:
revtrain = list(YelpReviews("training"))
print(len(revtrain), "training reviews")

## and shuffle just in case they are ordered
import numpy as np
229907 training reviews

Finally, write a function to generate sentences -- ordered lists of words -- from reviews that have certain star ratings

In [6]:
def StarSentences(reviews, stars=[1,2,3,4,5]):
    for r in reviews:
        if r['y'] in stars:
            for s in r['x']:
                yield s

Word2Vec modeling

We fit out-of-the-box Word2Vec

In [7]:
from gensim.models import Word2Vec
import multiprocessing

## create a w2v learner 
basemodel = Word2Vec(
    workers=multiprocessing.cpu_count(), # use your cores
    iter=3, # iter = sweeps of SGD through the data; more is better
    hs=1, negative=0 # we only have scoring for the hierarchical softmax setup
Word2Vec(vocab=0, size=100, alpha=0.025)

Build vocab from all sentences (you could also pre-train the base model from a neutral or un-labeled vocabulary)

In [8]:

Now, we will deep copy each base model and do star-specific training. This is where the big computations happen...

In [9]:
from copy import deepcopy
starmodels = [deepcopy(basemodel) for i in range(5)]
for i in range(5):
    slist = list(StarSentences(revtrain, [i+1]))
    print(i+1, "stars (", len(slist), ")")
    starmodels[i].train(  slist, total_examples=len(slist) )
1 stars ( 246207 )
2 stars ( 295371 )
3 stars ( 437718 )
4 stars ( 883235 )
5 stars ( 799704 )

Inversion of the distributed representations

At this point, we have 5 different word2vec language representations. Each 'model' has been trained conditional (i.e., limited to) text from a specific star rating. We will apply Bayes rule to go from p(text|stars) to p(stars|text).

For any new sentence we can obtain its likelihood (lhd; actually, the composite likelihood approximation; see the paper) using the score function in the word2vec class. We get the likelihood for each sentence in the first test review, then convert to a probability over star ratings. Every sentence in the review is evaluated separately and the final star rating of the review is an average vote of all the sentences. This is all in the following handy wrapper.

In [10]:
docprob takes two lists
* docs: a list of documents, each of which is a list of sentences
* models: the candidate word2vec models (each potential class)

it returns the array of class probabilities.  Everything is done in-memory.

import pandas as pd # for quick summing within doc

def docprob(docs, mods):
    # score() takes a list [s] of sentences here; could also be a sentence generator
    sentlist = [s for d in docs for s in d]
    # the log likelihood of each sentence in this review under each w2v representation
    llhd = np.array( [ m.score(sentlist, len(sentlist)) for m in mods ] )
    # now exponentiate to get likelihoods, 
    lhd = np.exp(llhd - llhd.max(axis=0)) # subtract row max to avoid numeric overload
    # normalize across models (stars) to get sentence-star probabilities
    prob = pd.DataFrame( (lhd/lhd.sum(axis=0)).transpose() )
    # and finally average the sentence probabilities to get the review probability
    prob["doc"] = [i for i,d in enumerate(docs) for s in d]
    prob = prob.groupby("doc").mean()
    return prob

Test set example

As an example, we apply the inversion on the full test set.

In [11]:
# read in the test set
revtest = list(YelpReviews("test"))
In [12]:
# get the probs (note we give docprob a list of lists of words, plus the models)
probs = docprob( [r['x'] for r in revtest], starmodels )
In [13]:
import matplotlib
In [14]:
%matplotlib inline

probpos = pd.DataFrame({"out-of-sample prob positive":probs[[3,4]].sum(axis=1), 
                        "true stars":[r['y'] for r in revtest]})
probpos.boxplot("out-of-sample prob positive",by="true stars", figsize=(12,5))
<matplotlib.axes._subplots.AxesSubplot at 0x1bde1f3c8>