Keras and NLTK

I've been doing a lot more Python hacking, especially around text mining and using the deep learning library Keras and NLTK. Normally I'd do most of my work in RapidMiner but I wanted to do some grunt work and learn something along the way.  It was really about educating myself on Recurrent Neural Networks (RNN) and doing it the hard way I guess.

Keras and NLTK

As usually I went to google to do some sleuthing about how to text mine using an LSTM implementation of Keras and boy did I find some goodies. The best tutorials are easy to understand and follow along. My introduction to Deep Learning with Keras was via Jason's excellent tutorial called Text Generation with LSTM Recurrent Neural Networks in Python with Keras. Jason took a every easy to bite approach to implementing Keras to read in the Alice In Wonderland book character by character and then try to generate some text in the 'style' of what was written before. It was a great Proof of Concept but fraught with some strange results. He acknowledges that and offers some additional guidance at the end of the tutorial, mainly removing punctuation and more training epochs. The text processing is one thing but the model optimization is another. Since I have a crappy laptop I can just forget about optimizing a Keras script, so I went the text process route and used NLTK. Now that I've been around the text mining/processing block a bunch of times, the NLTK python library makes more sense in this application. I much prefer using the RapidMiner Text Processing implementation for 90% of what I do with text but every so often you need something special and atypical.

Initial Results

The first results were terrible as my tweet can attest too!

lol. the results of my #deeplearning #keras poetry model: "thethethethethethethethethethethethethethethethethethethethethethethethethethe"

— Thomas Ott (@neuralmarket) August 10, 2017

So I added a short function to Jason's script that preprocesses a new file loaded with haikus. I removed all punctuation and stop words with the express goal of generating haiku. While this script was learning I started to dig around the Internet for some other interesting and related posts on LSTM's, NLTK and text generation until I found Click-O-Tron.  That cracked me up. Leave it to us humans to take some cool piece of technology and implement it for lulz.

Implementation

I have grandiose dreams of using this script so I would need to put it in production one day. This is where everything got to be a pain in the ass. My first thought was to run the training on  a smaller machine and then use the trained weights to autogenerate new haikus in a separate scripts. This is not an atypical type of implementation. Right now I don't care if this will take days to train. While Python is great in many ways, dealing with libraries on one machine might be different on another machine and hardware. Especially when dealing with GPU's and stuff like that.  It's gets tricky and annoying considering I work on many different workstations these days. I have a crappy little ACER laptop that I use to cron python scripts for my Twitter related work, which also happens to be an AMD processor. I do most of my 'hacking' on larger laptop that happens to have an Intel processor. To transfer my scripts from one machine to another I have to always make sure that every single Python package is installed on each machine. PITA! Despite these annoyances, I ended up learning A LOT about Deep Learning architecture, their application, and short comings. In the end, it's another tool in a Data Science toolkit, just don't expect it to be a miracle savior.

Additional reading list

  • http://h6o6.com/2013/03/using-python-and-the-nltk-to-find-haikus-in-the-public-twitter-stream/
  • https://github.com/fchollet/keras/blob/master/examples/lstm_text_generation.py

The Python Script

#http://machinelearningmastery.com/text-generation-lstm-recurrent-neural-networks-python-keras/

import numpy
import os
import sys
import nltk
from keras.models import Sequential
from keras.layers import Dense
from keras.layers import Dropout
from keras.layers import LSTM
from keras.callbacks import ModelCheckpoint
from keras.utils import np_utils
import string
from nltk.tokenize import RegexpTokenizer
from nltk.corpus import stopwords
import re

# look at https://gist.github.com/ameyavilankar/10347201#file-preprocess-py-L1

def preprocess(sentence):
    sentence = sentence.lower()
    tokenizer = RegexpTokenizer(r'\w+')
    tokens = tokenizer.tokenize(sentence)
    filtered_words = filter(lambda token: token not in stopwords.words('english'), tokens)
    return " ".join(filtered_words)

# load ascii text and covert to lowercase
filename = "haikus.txt"
sentence = open(filename).read()
#raw_text = raw_text.lower()
#raw_text = nltk.sent_tokenize(raw_text)

sentence = preprocess(sentence)

#print (sentence)

raw_text = sentence

#print (raw_text)

# create mapping of unique chars to integers
chars = sorted(list(set(raw_text)))

#print (chars)
char_to_int = dict((c, i) for i, c in enumerate(chars))

#print (char_to_int)

n_chars = len(raw_text)
n_vocab = len(chars)
print ("Total Characters: ", n_chars)
print ("Total Vocab: ", n_vocab)

# prepare the dataset of input to output pairs encoded as integers
seq_length = 300
dataX = []
dataY = []
for i in range(0, n_chars - seq_length, 1):
    seq_in = raw_text[i:i + seq_length]
    seq_out = raw_text[i + seq_length]
    dataX.append([char_to_int[char] for char in seq_in])
    dataY.append(char_to_int[seq_out])
n_patterns = len(dataX)
print ("Total Patterns: ", n_patterns)

# reshape X to be [samples, time steps, features]
X = numpy.reshape(dataX, (n_patterns, seq_length, 1))
# normalize
X = X / float(n_vocab)
# one hot encode the output variable
y = np_utils.to_categorical(dataY)

# define the LSTM model
model = Sequential()
model.add(LSTM(256, input_shape=(X.shape[1], X.shape[2]), return_sequences=True))
model.add(Dropout(0.2))
model.add(LSTM(256))
model.add(Dropout(0.2))
model.add(Dense(y.shape[1], activation='softmax'))
model.compile(loss='categorical_crossentropy', optimizer='adam')

# define the checkpoint
filepath="weights-improvement-{epoch:02d}-{loss:.4f}.hdf5"
checkpoint = ModelCheckpoint(filepath, monitor='loss', verbose=1, save_best_only=True, mode='min')
callbacks_list = [checkpoint]

model.fit(X, y, epochs=3, batch_size=256, callbacks=callbacks_list)
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