Latent Dirichlet allocation (LDA) in Spark

Question

I am trying to write a progrma in Spark for carrying out Latent Dirichlet allocation (LDA). This Spark documentation page provides a nice example for perfroming LDA on the sample data. Below is the program

from pyspark.mllib.clustering import LDA, LDAModel
from pyspark.mllib.linalg import Vectors

# Load and parse the data
data = sc.textFile("data/mllib/sample_lda_data.txt")
parsedData = data.map(lambda line: Vectors.dense([float(x) for x in line.strip().split(' ')]))
# Index documents with unique IDs
corpus = parsedData.zipWithIndex().map(lambda x: [x[1], x[0]]).cache()

# Cluster the documents into three topics using LDA
ldaModel = LDA.train(corpus, k=3)

# Output topics. Each is a distribution over words (matching word count vectors)
print("Learned topics (as distributions over vocab of " + str(ldaModel.vocabSize())
      + " words):")
topics = ldaModel.topicsMatrix()
for topic in range(3):
    print("Topic " + str(topic) + ":")
    for word in range(0, ldaModel.vocabSize()):
        print(" " + str(topics[word][topic]))

# Save and load model
ldaModel.save(sc, "target/org/apache/spark/PythonLatentDirichletAllocationExample/LDAModel")
sameModel = LDAModel\
    .load(sc, "target/org/apache/spark/PythonLatentDirichletAllocationExample/LDAModel")

The sample input (sample_lda_data.txt) used is as below

1 2 6 0 2 3 1 1 0 0 3
1 3 0 1 3 0 0 2 0 0 1
1 4 1 0 0 4 9 0 1 2 0
2 1 0 3 0 0 5 0 2 3 9
3 1 1 9 3 0 2 0 0 1 3
4 2 0 3 4 5 1 1 1 4 0
2 1 0 3 0 0 5 0 2 2 9
1 1 1 9 2 1 2 0 0 1 3
4 4 0 3 4 2 1 3 0 0 0
2 8 2 0 3 0 2 0 2 7 2
1 1 1 9 0 2 2 0 0 3 3
4 1 0 0 4 5 1 3 0 1 0

How do I modify the program to run in on a text data file containing text data instead of numbers? Let the sample file contain the following text.

Latent Dirichlet allocation (LDA) is a topic model which infers topics from a collection of text documents. LDA can be thought of as a clustering algorithm as follows:

Topics correspond to cluster centers, and documents correspond to examples (rows) in a dataset. Topics and documents both exist in a feature space, where feature vectors are vectors of word counts (bag of words). Rather than estimating a clustering using a traditional distance, LDA uses a function based on a statistical model of how text documents are generated.

prashanth prashanth · Accepted Answer · 2017-02-13T09:15:22

After doing some research, I am attempting to answer this question. Below is the sample code to perform LDA on a text document with real text data using Spark.

from pyspark.sql import SQLContext, Row
from pyspark.ml.feature import CountVectorizer
from pyspark.mllib.clustering import LDA, LDAModel
from pyspark.mllib.linalg import Vector, Vectors

path = "sample_text_LDA.txt"

data = sc.textFile(path).zipWithIndex().map(lambda (words,idd): Row(idd= idd, words = words.split(" ")))
docDF = spark.createDataFrame(data)
Vector = CountVectorizer(inputCol="words", outputCol="vectors")
model = Vector.fit(docDF)
result = model.transform(docDF)

corpus = result.select("idd", "vectors").rdd.map(lambda (x,y): [x,Vectors.fromML(y)]).cache()

# Cluster the documents into three topics using LDA
ldaModel = LDA.train(corpus, k=3,maxIterations=100,optimizer='online')
topics = ldaModel.topicsMatrix()
vocabArray = model.vocabulary

wordNumbers = 10  # number of words per topic
topicIndices = sc.parallelize(ldaModel.describeTopics(maxTermsPerTopic = wordNumbers))

def topic_render(topic):  # specify vector id of words to actual words
    terms = topic[0]
    result = []
    for i in range(wordNumbers):
        term = vocabArray[terms[i]]
        result.append(term)
    return result

topics_final = topicIndices.map(lambda topic: topic_render(topic)).collect()

for topic in range(len(topics_final)):
    print ("Topic" + str(topic) + ":")
    for term in topics_final[topic]:
        print (term)
    print ('\n')

The topics extracted on the text data as mentioned in the question is as below:

Latent Dirichlet allocation (LDA) in Spark

1 Answers