This tutorial shows how to train a character-level language model with a multilayer recurrent neural network. In particular, we will train a multilayer LSTM network that is able to generate President Obama's speeches.
We first download the dataset and show the first few characters.
import os
import urllib
import zipfile
if not os.path.exists("char_lstm.zip"):
urllib.urlretrieve("http://data.mxnet.io/data/char_lstm.zip", "char_lstm.zip")
with zipfile.ZipFile("char_lstm.zip","r") as f:
f.extractall("./")
with open('obama.txt', 'r') as f:
print f.read()[0:1000]
Call to Renewal Keynote Address Call to Renewal Pt 1Call to Renewal Part 2 TOPIC: Our Past, Our Future & Vision for America June 28, 2006 Call to Renewal' Keynote Address Complete Text Good morning. I appreciate the opportunity to speak here at the Call to R enewal's Building a Covenant for a New America conference. I've had the opportunity to take a look at your Covenant for a New Ame rica. It is filled with outstanding policies and prescriptions for much of what ails this country. So I'd like to congratulate yo u all on the thoughtful presentations you've given so far about poverty and justice in America, and for putting fire under the fe et of the political leadership here in Washington.But today I'd like to talk about the connection between religion and politics a nd perhaps offer some thoughts about how we can sort through some of the often bitter arguments that we've been seeing over the l ast several years.I do so because, as you all know, we can affirm the importance of povert
Then we define a few utility functions to pre-process the dataset.
def read_content(path):
with open(path) as ins:
return ins.read()
# Return a dict which maps each char into an unique int id
def build_vocab(path):
content = list(read_content(path))
idx = 1 # 0 is left for zero-padding
the_vocab = {}
for word in content:
if len(word) == 0:
continue
if not word in the_vocab:
the_vocab[word] = idx
idx += 1
return the_vocab
# Encode a sentence with int ids
def text2id(sentence, the_vocab):
words = list(sentence)
return [the_vocab[w] for w in words if len(w) > 0]
# build char vocabluary from input
vocab = build_vocab("./obama.txt")
print('vocab size = %d' %(len(vocab)))
vocab size = 83
import lstm
# Each line contains at most 129 chars.
seq_len = 129
# embedding dimension, which maps a character to a 256-dimension vector
num_embed = 256
# number of lstm layers
num_lstm_layer = 3
# hidden unit in LSTM cell
num_hidden = 512
symbol = lstm.lstm_unroll(
num_lstm_layer,
seq_len,
len(vocab) + 1,
num_hidden=num_hidden,
num_embed=num_embed,
num_label=len(vocab) + 1,
dropout=0.2)
"""test_seq_len"""
data_file = open("./obama.txt")
for line in data_file:
assert len(line) <= seq_len + 1, "seq_len is smaller than maximum line length. Current line length is %d. Line content is: %s" % (len(line), line)
data_file.close()
First, we create a DataIterator
import bucket_io
# The batch size for training
batch_size = 32
# initalize states for LSTM
init_c = [('l%d_init_c'%l, (batch_size, num_hidden)) for l in range(num_lstm_layer)]
init_h = [('l%d_init_h'%l, (batch_size, num_hidden)) for l in range(num_lstm_layer)]
init_states = init_c + init_h
# Even though BucketSentenceIter supports various length examples,
# we simply use the fixed length version here
data_train = bucket_io.BucketSentenceIter(
"./obama.txt",
vocab,
[seq_len],
batch_size,
init_states,
seperate_char='\n',
text2id=text2id,
read_content=read_content)
Summary of dataset ================== bucket of len 129 : 8290 samples
Then we can train with the standard model.fit
approach.
# @@@ AUTOTEST_OUTPUT_IGNORED_CELL
import mxnet as mx
import numpy as np
import logging
logging.getLogger().setLevel(logging.DEBUG)
# We will show a quick demo with only 1 epoch. In practice, we can set it to be 100
num_epoch = 1
# learning rate
learning_rate = 0.01
# Evaluation metric
def Perplexity(label, pred):
loss = 0.
for i in range(pred.shape[0]):
loss += -np.log(max(1e-10, pred[i][int(label[i])]))
return np.exp(loss / label.size)
model = mx.mod.Module(symbol=symbol,
data_names=[x[0] for x in data_train.provide_data],
label_names=[y[0] for y in data_train.provide_label],
context=[mx.gpu(0)])
model.fit(train_data=data_train,
num_epoch=num_epoch,
optimizer='sgd',
optimizer_params={'learning_rate':learning_rate, 'momentum':0, 'wd':0.0001},
initializer=mx.init.Xavier(factor_type="in", magnitude=2.34),
eval_metric=mx.metric.np(Perplexity),
batch_end_callback=mx.callback.Speedometer(batch_size, 20),
epoch_end_callback=mx.callback.do_checkpoint("obama"))
INFO:root:Start training with [gpu(0)] INFO:root:Epoch[0] Batch [20] Speed: 74.29 samples/sec Train-Perplexity=38.179584 INFO:root:Epoch[0] Batch [40] Speed: 71.11 samples/sec Train-Perplexity=24.131196 INFO:root:Epoch[0] Batch [60] Speed: 71.25 samples/sec Train-Perplexity=23.802137 INFO:root:Epoch[0] Batch [80] Speed: 70.94 samples/sec Train-Perplexity=23.195673 INFO:root:Epoch[0] Batch [100] Speed: 71.35 samples/sec Train-Perplexity=22.974986 INFO:root:Epoch[0] Batch [120] Speed: 71.11 samples/sec Train-Perplexity=22.783410 INFO:root:Epoch[0] Batch [140] Speed: 71.04 samples/sec Train-Perplexity=22.826977 INFO:root:Epoch[0] Batch [160] Speed: 71.15 samples/sec Train-Perplexity=22.681599 INFO:root:Epoch[0] Batch [180] Speed: 71.31 samples/sec Train-Perplexity=22.268179 INFO:root:Epoch[0] Batch [200] Speed: 71.16 samples/sec Train-Perplexity=22.548455 INFO:root:Epoch[0] Batch [220] Speed: 71.29 samples/sec Train-Perplexity=22.224348 INFO:root:Epoch[0] Batch [240] Speed: 71.10 samples/sec Train-Perplexity=22.563747 INFO:root:Epoch[0] Resetting Data Iterator INFO:root:Epoch[0] Time cost=116.385 INFO:root:Saved checkpoint to "obama-0001.params"
We first define some utility functions to help us make inferences:
from rnn_model import LSTMInferenceModel
# helper strcuture for prediction
def MakeRevertVocab(vocab):
dic = {}
for k, v in vocab.items():
dic[v] = k
return dic
# make input from char
def MakeInput(char, vocab, arr):
idx = vocab[char]
tmp = np.zeros((1,))
tmp[0] = idx
arr[:] = tmp
# helper function for random sample
def _cdf(weights):
total = sum(weights)
result = []
cumsum = 0
for w in weights:
cumsum += w
result.append(cumsum / total)
return result
def _choice(population, weights):
assert len(population) == len(weights)
cdf_vals = _cdf(weights)
x = random.random()
idx = bisect.bisect(cdf_vals, x)
return population[idx]
# we can use random output or fixed output by choosing largest probability
def MakeOutput(prob, vocab, sample=False, temperature=1.):
if sample == False:
idx = np.argmax(prob, axis=1)[0]
else:
fix_dict = [""] + [vocab[i] for i in range(1, len(vocab) + 1)]
scale_prob = np.clip(prob, 1e-6, 1 - 1e-6)
rescale = np.exp(np.log(scale_prob) / temperature)
rescale[:] /= rescale.sum()
return _choice(fix_dict, rescale[0, :])
try:
char = vocab[idx]
except:
char = ''
return char
Then we create the inference model:
import rnn_model
# load from check-point
_, arg_params, __ = mx.model.load_checkpoint("obama", 75)
# build an inference model
model = rnn_model.LSTMInferenceModel(
num_lstm_layer,
len(vocab) + 1,
num_hidden=num_hidden,
num_embed=num_embed,
num_label=len(vocab) + 1,
arg_params=arg_params,
ctx=mx.gpu(),
dropout=0.2)
Now we can generate a sequence of 600 characters starting with "The United States"
seq_length = 600
input_ndarray = mx.nd.zeros((1,))
revert_vocab = MakeRevertVocab(vocab)
# Feel free to change the starter sentence
output ='The United States'
random_sample = False
new_sentence = True
ignore_length = len(output)
for i in range(seq_length):
if i <= ignore_length - 1:
MakeInput(output[i], vocab, input_ndarray)
else:
MakeInput(output[-1], vocab, input_ndarray)
prob = model.forward(input_ndarray, new_sentence)
new_sentence = False
next_char = MakeOutput(prob, revert_vocab, random_sample)
if next_char == '':
new_sentence = True
if i >= ignore_length - 1:
output += next_char
print(output)
The United States of America. That's why I'm running for President.The first place we can do better than that they can afford to get the that they can afford to differ on the part of the political settlement. The second part of the problem is that the consequences would have to see the chance to starthe country that we can start by the challenges of the American people. The American people have been talking about how to compete with the streets of San Antonio who are serious about the courage to come together as one people. That the American people have been trying to get there. And they say