# coding=utf-8
"""Latent Dirichlet allocation using collapsed Gibbs sampling"""
from __future__ import absolute_import, division, unicode_literals # noqa
import logging
import sys
import numpy as np
import lda._lda
import lda.utils
logger = logging.getLogger('lda')
PY2 = sys.version_info[0] == 2
if PY2:
range = xrange
class LDA:
"""Latent Dirichlet allocation using collapsed Gibbs sampling
参数设置
----------
n_topics : int
主题topic数量
n_iter : int, default 2000
采样迭代次数
alpha : float, default 0.1
主题的狄利克雷先验分布参数
eta : float, default 0.01
词的狄利克雷先验分布参数
random_state : int or RandomState, optional
The generator used for the initial topics.
Attributes
----------
`components_` : array, shape = [n_topics, n_features]
Point estimate of the topic-word distributions (Phi in literature)
`topic_word_` :
Alias for `components_`
`nzw_` : array, shape = [n_topics, n_features]
Matrix of counts recording topic-word assignments in final iteration.
`ndz_` : array, shape = [n_samples, n_topics]
Matrix of counts recording document-topic assignments in final iteration.
`doc_topic_` : array, shape = [n_samples, n_features]
Point estimate of the document-topic distributions (Theta in literature)
`nz_` : array, shape = [n_topics]
Array of topic assignment counts in final iteration.
Examples
--------
>>> import numpy
>>> X = numpy.array([[1,1], [2, 1], [3, 1], [4, 1], [5, 8], [6, 1]])
>>> import lda
>>> model = lda.LDA(n_topics=2, random_state=0, n_iter=100)
>>> model.fit(X) #doctest: +ELLIPSIS +NORMALIZE_WHITESPACE
LDA(alpha=...
>>> model.components_
array([[ 0.85714286, 0.14285714],
[ 0.45 , 0.55 ]])
>>> model.loglikelihood() #doctest: +ELLIPSIS
-40.395...
References
----------
Blei, David M., Andrew Y. Ng, and Michael I. Jordan. "Latent Dirichlet
Allocation." Journal of Machine Learning Research 3 (2003): 993–1022.
Griffiths, Thomas L., and Mark Steyvers. "Finding Scientific Topics."
Proceedings of the National Academy of Sciences 101 (2004): 5228–5235.
doi:10.1073/pnas.0307752101.
Wallach, Hanna, David Mimno, and Andrew McCallum. "Rethinking LDA: Why
Priors Matter." In Advances in Neural Information Processing Systems 22,
edited by Y. Bengio, D. Schuurmans, J. Lafferty, C. K. I. Williams, and A.
Culotta, 1973–1981, 2009.
Buntine, Wray. "Estimating Likelihoods for Topic Models." In Advances in
Machine Learning, First Asian Conference on Machine Learning (2009): 51–64.
doi:10.1007/978-3-642-05224-8_6.
"""
def __init__(self, n_topics, n_iter=2000, alpha=0.1, eta=0.01, random_state=None,
refresh=10):
self.n_topics = n_topics
self.n_iter = n_iter
self.alpha = alpha
self.eta = eta
# if random_state is None, check_random_state(None) does nothing
# other than return the current numpy RandomState
self.random_state = random_state
self.refresh = refresh
if alpha <= 0 or eta <= 0:
raise ValueError("alpha and eta must be greater than zero")
# random numbers that are reused
rng = lda.utils.check_random_state(random_state)
self._rands = rng.rand(1024**2 // 8) # 1MiB of random variates
# configure console logging if not already configured
if len(logger.handlers) == 1 and isinstance(logger.handlers[0], logging.NullHandler):
logging.basicConfig(level=logging.INFO)
def fit(self, X, y=None):
"""Fit the model with X.
Parameters
----------
X: array-like, shape (n_samples, n_features)
Training data, where n_samples in the number of samples
and n_features is the number of features. Sparse matrix allowed.
Returns
-------
self : object
Returns the instance itself.
"""
self._fit(X)
return self
def fit_transform(self, X, y=None):
"""Apply dimensionality reduction on X
Parameters
----------
X : array-like, shape (n_samples, n_features)
New data, where n_samples in the number of samples
and n_features is the number of features. Sparse matrix allowed.
Returns
-------
doc_topic : array-like, shape (n_samples, n_topics)
Point estimate of the document-topic distributions
"""
if isinstance(X, np.ndarray):
# in case user passes a (non-sparse) array of shape (n_features,)
# turn it into an array of shape (1, n_features)
X = np.atleast_2d(X)
self._fit(X)
return self.doc_topic_
def transform(self, X, max_iter=20, tol=1e-16):
"""Transform the data X according to previously fitted model
Parameters
----------
X : array-like, shape (n_samples, n_features)
New data, where n_samples in the number of samples
and n_features is the number of features.
max_iter : int, optional
Maximum number of iterations in iterated-pseudocount estimation.
tol: double, optional
Tolerance value used in stopping condition.
Returns
-------
doc_topic : array-like, shape (n_samples, n_topics)
Point estimate of the document-topic distributions
Note
----
This uses the "iterated pseudo-counts" approach described
in Wallach et al. (2009) and discussed in Buntine (2009).
"""
if isinstance(X, np.ndarray):
# in case user passes a (non-sparse) array of shape (n_features,)
# turn it into an array of shape (1, n_features)
X = np.atleast_2d(X)
doc_topic = np.empty((X.shape[0], self.n_topics))
WS, DS = lda.utils.matrix_to_lists(X)
# TODO: this loop is parallelizable
for d in np.unique(DS):
doc_topic[d] = self._transform_single(WS[DS == d], max_iter, tol)
return doc_topic
def _transform_single(self, doc, max_iter, tol):
"""Transform a single document according to the previously fit model
Parameters
----------
X : 1D numpy array of integers
Each element represents a word in the document
max_iter : int
Maximum number of iterations in iterated-pseudocount estimation.
tol: double
Tolerance value used in stopping condition.
Returns
-------
doc_topic : 1D numpy array of length n_topics
Point estimate of the topic distributions for document
Note
----
See Note in `transform` documentation.
"""
PZS = np.zeros((len(doc), self.n_topics))
for iteration in range(max_iter + 1): # +1 is for initialization
PZS_new = self.components_[:, doc].T
PZS_new *= (PZS.sum(axis=0) - PZS + self.alpha)
PZS_new /= PZS_new.sum(axis=1)[:, np.newaxis] # vector to single column matrix
delta_naive = np.abs(PZS_new - PZS).sum()
logger.debug('transform iter {}, delta {}'.format(iteration, delta_naive))
PZS = PZS_new
if delta_naive < tol:
break
theta_doc = PZS.sum(axis=0) / PZS.sum()
assert len(theta_doc) == self.n_topics
assert theta_doc.shape == (self.n_topics,)
return theta_doc
def _transform_single(self, doc, max_iter, tol):
"""Transform a single document according to the previously fit model
Parameters
----------
X : 1D numpy array of integers
Each element represents a word in the document
max_iter : int
Maximum number of iterations in iterated-pseudocount estimation.
tol: double
Tolerance value used in stopping condition.
Returns
-------
doc_topic : 1D numpy array of length n_topics
Point estimate of the topic distributions for document
Note
----
See Note in `transform` documentation.
"""
PZS = np.zeros((len(doc), self.n_topics))
for iteration in range(max_iter + 1): # +1 is for initialization
PZS_new = self.components_[:, doc].T
PZS_new *= (PZS.sum(axis=0) - PZS + self.alpha)
PZS_new /= PZS_new.sum(axis=1)[:, np.newaxis] # vector to single column matrix
delta_naive = np.abs(PZS_new - PZS).sum()
logger.debug('transform iter {}, delta {}'.format(iteration, delta_naive))
PZS = PZS_new
if delta_naive < tol:
break
theta_doc = PZS.sum(axis=0) / PZS.sum()
assert len(theta_doc) == self.n_topics
assert theta_doc.shape == (self.n_topics,)
return theta_doc
def _fit(self, X):
"""Fit the model to the data X
Parameters
----------
X: array-like, shape (n_samples, n_features)
Training vector, where n_samples in the number of samples and
n_features is the number of features. Sparse matrix allowed.
"""
random_state = lda.utils.check_random_state(self.random_state)
rands = self._rands.copy()
self._initialize(X)
for it in range(self.n_iter):
# FIXME: using numpy.roll with a random shift might be faster
random_state.shuffle(rands)
if it % self.refresh == 0:
ll = self.loglikelihood()
logger.info("<{}> log likelihood: {:.0f}".format(it, ll))
# keep track of loglikelihoods for monitoring convergence
self.loglikelihoods_.append(ll)
self._sample_topics(rands)
ll = self.loglikelihood()
logger.info("<{}> log likelihood: {:.0f}".format(self.n_iter - 1, ll))
# note: numpy /= is integer division
self.components_ = (self.nzw_ + self.eta).astype(float)
self.components_ /= np.sum(self.components_, axis=1)[:, np.newaxis]
self.topic_word_ = self.components_
self.doc_topic_ = (self.ndz_ + self.alpha).astype(float)
self.doc_topic_ /= np.sum(self.doc_topic_, axis=1)[:, np.newaxis]
# delete attributes no longer needed after fitting to save memory and reduce clutter
del self.WS
del self.DS
del self.ZS
return self
def _initialize(self, X):
D, W = X.shape
N = int(X.sum())
n_topics = self.n_topics
n_iter = self.n_iter
logger.info("n_documents: {}".format(D))
logger.info("vocab_size: {}".format(W))
logger.info("n_words: {}".format(N))
logger.info("n_topics: {}".format(n_topics))
logger.info("n_iter: {}".format(n_iter))
self.nzw_ = nzw_ = np.zeros((n_topics, W), dtype=np.intc)
self.ndz_ = ndz_ = np.zeros((D, n_topics), dtype=np.intc)
self.nz_ = nz_ = np.zeros(n_topics, dtype=np.intc)
self.WS, self.DS = WS, DS = lda.utils.matrix_to_lists(X)
self.ZS = ZS = np.empty_like(self.WS, dtype=np.intc)
np.testing.assert_equal(N, len(WS))
for i in range(N):
w, d = WS[i], DS[i]
z_new = i % n_topics
ZS[i] = z_new
ndz_[d, z_new] += 1
nzw_[z_new, w] += 1
nz_[z_new] += 1
self.loglikelihoods_ = []
def loglikelihood(self):
"""Calculate complete log likelihood, log p(w,z)
Formula used is log p(w,z) = log p(w|z) + log p(z)
"""
nzw, ndz, nz = self.nzw_, self.ndz_, self.nz_
alpha = self.alpha
eta = self.eta
nd = np.sum(ndz, axis=1).astype(np.intc)
return lda._lda._loglikelihood(nzw, ndz, nz, nd, alpha, eta)
def _sample_topics(self, rands):
"""Samples all topic assignments. Called once per iteration."""
n_topics, vocab_size = self.nzw_.shape
alpha = np.repeat(self.alpha, n_topics).astype(np.float64)
eta = np.repeat(self.eta, vocab_size).astype(np.float64)
lda._lda._sample_topics(self.WS, self.DS, self.ZS, self.nzw_, self.ndz_, self.nz_,
alpha, eta, rands)
LDA主题模型Python源码实现
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