models.ldamulticore
– parallelized Latent Dirichlet Allocation¶
Online Latent Dirichlet Allocation (LDA) in Python, using all CPU cores to parallelize and speed up model training.
The parallelization uses multiprocessing; in case this doesn’t work for you for some reason,
try the gensim.models.ldamodel.LdaModel
class which is an equivalent, but more straightforward and singlecore
implementation.
The training algorithm:
is streamed: training documents may come in sequentially, no random access required,
runs in constant memory w.r.t. the number of documents: size of the training corpus does not affect memory footprint, can process corpora larger than RAM
Wallclock performance on the English Wikipedia (2G corpus positions, 3.5M documents, 100K features, 0.54G nonzero entries in the final bagofwords matrix), requesting 100 topics:
algorithm 
training time 

LdaMulticore(workers=1) 
2h30m 
LdaMulticore(workers=2) 
1h24m 
LdaMulticore(workers=3) 
1h6m 
old LdaModel() 
3h44m 
simply iterating over input corpus = I/O overhead 
20m 
(Measured on this i7 server with 4 physical cores, so that optimal workers=3, one less than the number of cores.)
This module allows both LDA model estimation from a training corpus and inference of topic distribution on new, unseen documents. The model can also be updated with new documents for online training.
The core estimation code is based on the onlineldavb.py script, by Hoffman, Blei, Bach: Online Learning for Latent Dirichlet Allocation, NIPS 2010.
Usage examples¶
The constructor estimates Latent Dirichlet Allocation model parameters based on a training corpus
>>> from gensim.test.utils import common_corpus, common_dictionary
>>>
>>> lda = LdaMulticore(common_corpus, id2word=common_dictionary, num_topics=10)
Save a model to disk, or reload a pretrained model
>>> from gensim.test.utils import datapath
>>>
>>> # Save model to disk.
>>> temp_file = datapath("model")
>>> lda.save(temp_file)
>>>
>>> # Load a potentially pretrained model from disk.
>>> lda = LdaModel.load(temp_file)
Query, or update the model using new, unseen documents
>>> other_texts = [
... ['computer', 'time', 'graph'],
... ['survey', 'response', 'eps'],
... ['human', 'system', 'computer']
... ]
>>> other_corpus = [common_dictionary.doc2bow(text) for text in other_texts]
>>>
>>> unseen_doc = other_corpus[0]
>>> vector = lda[unseen_doc] # get topic probability distribution for a document
>>>
>>> # Update the model by incrementally training on the new corpus.
>>> lda.update(other_corpus) # update the LDA model with additional documents

class
gensim.models.ldamulticore.
LdaMulticore
(corpus=None, num_topics=100, id2word=None, workers=None, chunksize=2000, passes=1, batch=False, alpha='symmetric', eta=None, decay=0.5, offset=1.0, eval_every=10, iterations=50, gamma_threshold=0.001, random_state=None, minimum_probability=0.01, minimum_phi_value=0.01, per_word_topics=False, dtype=<class 'numpy.float32'>)¶ Bases:
gensim.models.ldamodel.LdaModel
An optimized implementation of the LDA algorithm, able to harness the power of multicore CPUs. Follows the similar API as the parent class
LdaModel
. Parameters
corpus ({iterable of list of (int, float), scipy.sparse.csc}, optional) – Stream of document vectors or sparse matrix of shape (num_documents, num_terms). If not given, the model is left untrained (presumably because you want to call
update()
manually).num_topics (int, optional) – The number of requested latent topics to be extracted from the training corpus.
id2word ({dict of (int, str),
gensim.corpora.dictionary.Dictionary
}) – Mapping from word IDs to words. It is used to determine the vocabulary size, as well as for debugging and topic printing.workers (int, optional) – Number of workers processes to be used for parallelization. If None all available cores (as estimated by workers=cpu_count()1 will be used. Note however that for hyperthreaded CPUs, this estimation returns a too high number – set workers directly to the number of your real cores (not hyperthreads) minus one, for optimal performance.
chunksize (int, optional) – Number of documents to be used in each training chunk.
passes (int, optional) – Number of passes through the corpus during training.
alpha ({np.ndarray, str}, optional) –
Can be set to an 1D array of length equal to the number of expected topics that expresses our apriori belief for the each topics’ probability. Alternatively default prior selecting strategies can be employed by supplying a string:
’asymmetric’: Uses a fixed normalized asymmetric prior of 1.0 / topicno.
eta ({float, np.array, str}, optional) –
Apriori belief on word probability, this can be:
scalar for a symmetric prior over topic/word probability,
vector of length num_words to denote an asymmetric user defined probability for each word,
matrix of shape (num_topics, num_words) to assign a probability for each wordtopic combination,
the string ‘auto’ to learn the asymmetric prior from the data.
decay (float, optional) – A number between (0.5, 1] to weight what percentage of the previous lambda value is forgotten when each new document is examined. Corresponds to Kappa from Matthew D. Hoffman, David M. Blei, Francis Bach: “Online Learning for Latent Dirichlet Allocation NIPS‘10”.
offset (float, optional) –
Hyperparameter that controls how much we will slow down the first steps the first few iterations. Corresponds to Tau_0 from Matthew D. Hoffman, David M. Blei, Francis Bach: “Online Learning for Latent Dirichlet Allocation NIPS‘10”.
eval_every (int, optional) – Log perplexity is estimated every that many updates. Setting this to one slows down training by ~2x.
iterations (int, optional) – Maximum number of iterations through the corpus when inferring the topic distribution of a corpus.
gamma_threshold (float, optional) – Minimum change in the value of the gamma parameters to continue iterating.
minimum_probability (float, optional) – Topics with a probability lower than this threshold will be filtered out.
random_state ({np.random.RandomState, int}, optional) – Either a randomState object or a seed to generate one. Useful for reproducibility.
minimum_phi_value (float, optional) – if per_word_topics is True, this represents a lower bound on the term probabilities.
per_word_topics (bool) – If True, the model also computes a list of topics, sorted in descending order of most likely topics for each word, along with their phi values multiplied by the feature length (i.e. word count).
dtype ({numpy.float16, numpy.float32, numpy.float64}, optional) – Datatype to use during calculations inside model. All inputs are also converted.

bound
(corpus, gamma=None, subsample_ratio=1.0)¶ Estimate the variational bound of documents from the corpus as E_q[log p(corpus)]  E_q[log q(corpus)].
 Parameters
corpus (iterable of list of (int, float), optional) – Stream of document vectors or sparse matrix of shape (num_documents, num_terms) used to estimate the variational bounds.
gamma (numpy.ndarray, optional) – Topic weight variational parameters for each document. If not supplied, it will be inferred from the model.
subsample_ratio (float, optional) – Percentage of the whole corpus represented by the passed corpus argument (in case this was a sample). Set to 1.0 if the whole corpus was passed.This is used as a multiplicative factor to scale the likelihood appropriately.
 Returns
The variational bound score calculated for each document.
 Return type
numpy.ndarray

clear
()¶ Clear the model’s state to free some memory. Used in the distributed implementation.

diff
(other, distance='kullback_leibler', num_words=100, n_ann_terms=10, diagonal=False, annotation=True, normed=True)¶ Calculate the difference in topic distributions between two models: self and other.
 Parameters
other (
LdaModel
) – The model which will be compared against the current object.distance ({'kullback_leibler', 'hellinger', 'jaccard', 'jensen_shannon'}) – The distance metric to calculate the difference with.
num_words (int, optional) – The number of most relevant words used if distance == ‘jaccard’. Also used for annotating topics.
n_ann_terms (int, optional) – Max number of words in intersection/symmetric difference between topics. Used for annotation.
diagonal (bool, optional) – Whether we need the difference between identical topics (the diagonal of the difference matrix).
annotation (bool, optional) – Whether the intersection or difference of words between two topics should be returned.
normed (bool, optional) – Whether the matrix should be normalized or not.
 Returns
numpy.ndarray – A difference matrix. Each element corresponds to the difference between the two topics, shape (self.num_topics, other.num_topics)
numpy.ndarray, optional – Annotation matrix where for each pair we include the word from the intersection of the two topics, and the word from the symmetric difference of the two topics. Only included if annotation == True. Shape (self.num_topics, other_model.num_topics, 2).
Examples
Get the differences between each pair of topics inferred by two models
>>> from gensim.models.ldamulticore import LdaMulticore >>> from gensim.test.utils import datapath >>> >>> m1 = LdaMulticore.load(datapath("lda_3_0_1_model")) >>> m2 = LdaMulticore.load(datapath("ldamodel_python_3_5")) >>> mdiff, annotation = m1.diff(m2) >>> topic_diff = mdiff # get matrix with difference for each topic pair from `m1` and `m2`

do_estep
(chunk, state=None)¶ Perform inference on a chunk of documents, and accumulate the collected sufficient statistics.
 Parameters
chunk (list of list of (int, float)) – The corpus chunk on which the inference step will be performed.
state (
LdaState
, optional) – The state to be updated with the newly accumulated sufficient statistics. If none, the models self.state is updated.
 Returns
Gamma parameters controlling the topic weights, shape (len(chunk), self.num_topics).
 Return type
numpy.ndarray

do_mstep
(rho, other, extra_pass=False)¶ Maximization step: use linear interpolation between the existing topics and collected sufficient statistics in other to update the topics.
 Parameters
rho (float) – Learning rate.
other (
LdaModel
) – The model whose sufficient statistics will be used to update the topics.extra_pass (bool, optional) – Whether this step required an additional pass over the corpus.

get_document_topics
(bow, minimum_probability=None, minimum_phi_value=None, per_word_topics=False)¶ Get the topic distribution for the given document.
 Parameters
bow (corpus : list of (int, float)) – The document in BOW format.
minimum_probability (float) – Topics with an assigned probability lower than this threshold will be discarded.
minimum_phi_value (float) –
 If per_word_topics is True, this represents a lower bound on the term probabilities that are included.
If set to None, a value of 1e8 is used to prevent 0s.
per_word_topics (bool) – If True, this function will also return two extra lists as explained in the “Returns” section.
 Returns
list of (int, float) – Topic distribution for the whole document. Each element in the list is a pair of a topic’s id, and the probability that was assigned to it.
list of (int, list of (int, float), optional – Most probable topics per word. Each element in the list is a pair of a word’s id, and a list of topics sorted by their relevance to this word. Only returned if per_word_topics was set to True.
list of (int, list of float), optional – Phi relevance values, multiplied by the feature length, for each wordtopic combination. Each element in the list is a pair of a word’s id and a list of the phi values between this word and each topic. Only returned if per_word_topics was set to True.

get_term_topics
(word_id, minimum_probability=None)¶ Get the most relevant topics to the given word.
 Parameters
word_id (int) – The word for which the topic distribution will be computed.
minimum_probability (float, optional) – Topics with an assigned probability below this threshold will be discarded.
 Returns
The relevant topics represented as pairs of their ID and their assigned probability, sorted by relevance to the given word.
 Return type
list of (int, float)

get_topic_terms
(topicid, topn=10)¶ Get the representation for a single topic. Words the integer IDs, in constrast to
show_topic()
that represents words by the actual strings. Parameters
topicid (int) – The ID of the topic to be returned
topn (int, optional) – Number of the most significant words that are associated with the topic.
 Returns
Word ID  probability pairs for the most relevant words generated by the topic.
 Return type
list of (int, float)

get_topics
()¶ Get the termtopic matrix learned during inference.
 Returns
The probability for each word in each topic, shape (num_topics, vocabulary_size).
 Return type
numpy.ndarray

inference
(chunk, collect_sstats=False)¶ Given a chunk of sparse document vectors, estimate gamma (parameters controlling the topic weights) for each document in the chunk.
This function does not modify the model The whole input chunk of document is assumed to fit in RAM; chunking of a large corpus must be done earlier in the pipeline. Avoids computing the phi variational parameter directly using the optimization presented in Lee, Seung: Algorithms for nonnegative matrix factorization”.
 Parameters
chunk (list of list of (int, float)) – The corpus chunk on which the inference step will be performed.
collect_sstats (bool, optional) – If set to True, also collect (and return) sufficient statistics needed to update the model’s topicword distributions.
 Returns
The first element is always returned and it corresponds to the states gamma matrix. The second element is only returned if collect_sstats == True and corresponds to the sufficient statistics for the M step.
 Return type
(numpy.ndarray, {numpy.ndarray, None})

init_dir_prior
(prior, name)¶ Initialize priors for the Dirichlet distribution.
 Parameters
prior ({str, list of float, numpy.ndarray of float, float}) –
Apriori belief on word probability. If name == ‘eta’ then the prior can be:
scalar for a symmetric prior over topic/word probability,
vector of length num_words to denote an asymmetric user defined probability for each word,
matrix of shape (num_topics, num_words) to assign a probability for each wordtopic combination,
the string ‘auto’ to learn the asymmetric prior from the data.
If name == ‘alpha’, then the prior can be:
an 1D array of length equal to the number of expected topics,
’symmetric’: Uses a fixed symmetric prior per topic,
’asymmetric’: Uses a fixed normalized asymmetric prior of 1.0 / (topic_index + sqrt(num_topics)),
’auto’: Learns an asymmetric prior from the corpus.
name ({'alpha', 'eta'}) – Whether the prior is parameterized by the alpha vector (1 parameter per topic) or by the eta (1 parameter per unique term in the vocabulary).

classmethod
load
(fname, *args, **kwargs)¶ Load a previously saved
gensim.models.ldamodel.LdaModel
from file.See also
save()
Save model.
 Parameters
Examples
Large arrays can be memmap’ed back as readonly (shared memory) by setting mmap=’r’:
>>> from gensim.test.utils import datapath >>> >>> fname = datapath("lda_3_0_1_model") >>> lda = LdaModel.load(fname, mmap='r')

log_perplexity
(chunk, total_docs=None)¶ Calculate and return perword likelihood bound, using a chunk of documents as evaluation corpus.
Also output the calculated statistics, including the perplexity=2^(bound), to log at INFO level.
 Parameters
chunk (list of list of (int, float)) – The corpus chunk on which the inference step will be performed.
total_docs (int, optional) – Number of docs used for evaluation of the perplexity.
 Returns
The variational bound score calculated for each word.
 Return type
numpy.ndarray

print_topic
(topicno, topn=10)¶ Get a single topic as a formatted string.
 Parameters
topicno (int) – Topic id.
topn (int) – Number of words from topic that will be used.
 Returns
String representation of topic, like ‘0.340 * “category” + 0.298 * “$M$” + 0.183 * “algebra” + … ‘.
 Return type
str

print_topics
(num_topics=20, num_words=10)¶ Get the most significant topics (alias for show_topics() method).
 Parameters
num_topics (int, optional) – The number of topics to be selected, if 1  all topics will be in result (ordered by significance).
num_words (int, optional) – The number of words to be included per topics (ordered by significance).
 Returns
Sequence with (topic_id, [(word, value), … ]).
 Return type
list of (int, list of (str, float))

save
(fname, ignore=('state', 'dispatcher'), separately=None, *args, **kwargs)¶ Save the model to a file.
Large internal arrays may be stored into separate files, with fname as prefix.
Notes
If you intend to use models across Python 2/3 versions there are a few things to keep in mind:
The pickled Python dictionaries will not work across Python versions
The save method does not automatically save all numpy arrays separately, only those ones that exceed sep_limit set in
save()
. The main concern here is the alpha array if for instance using alpha=’auto’.
Please refer to the wiki recipes section for an example on how to work around these issues.
See also
load()
Load model.
 Parameters
fname (str) – Path to the system file where the model will be persisted.
ignore (tuple of str, optional) – The named attributes in the tuple will be left out of the pickled model. The reason why the internal state is ignored by default is that it uses its own serialisation rather than the one provided by this method.
separately ({list of str, None}, optional) – If None  automatically detect large numpy/scipy.sparse arrays in the object being stored, and store them into separate files. This avoids pickle memory errors and allows mmap’ing large arrays back on load efficiently. If list of str  this attributes will be stored in separate files, the automatic check is not performed in this case.
*args – Positional arguments propagated to
save()
.**kwargs – Key word arguments propagated to
save()
.

show_topic
(topicid, topn=10)¶ Get the representation for a single topic. Words here are the actual strings, in constrast to
get_topic_terms()
that represents words by their vocabulary ID. Parameters
topicid (int) – The ID of the topic to be returned
topn (int, optional) – Number of the most significant words that are associated with the topic.
 Returns
Word  probability pairs for the most relevant words generated by the topic.
 Return type
list of (str, float)

show_topics
(num_topics=10, num_words=10, log=False, formatted=True)¶ Get a representation for selected topics.
 Parameters
num_topics (int, optional) – Number of topics to be returned. Unlike LSA, there is no natural ordering between the topics in LDA. The returned topics subset of all topics is therefore arbitrary and may change between two LDA training runs.
num_words (int, optional) – Number of words to be presented for each topic. These will be the most relevant words (assigned the highest probability for each topic).
log (bool, optional) – Whether the output is also logged, besides being returned.
formatted (bool, optional) – Whether the topic representations should be formatted as strings. If False, they are returned as 2 tuples of (word, probability).
 Returns
a list of topics, each represented either as a string (when formatted == True) or wordprobability pairs.
 Return type
list of {str, tuple of (str, float)}

sync_state
(current_Elogbeta=None)¶ Propagate the states topic probabilities to the inner object’s attribute.
 Parameters
current_Elogbeta (numpy.ndarray) – Posterior probabilities for each topic, optional. If omitted, it will get Elogbeta from state.

top_topics
(corpus=None, texts=None, dictionary=None, window_size=None, coherence='u_mass', topn=20, processes=1)¶ Get the topics with the highest coherence score the coherence for each topic.
 Parameters
corpus (iterable of list of (int, float), optional) – Corpus in BoW format.
texts (list of list of str, optional) – Tokenized texts, needed for coherence models that use sliding window based (i.e. coherence=`c_something`) probability estimator .
dictionary (
Dictionary
, optional) – Gensim dictionary mapping of id word to create corpus. If model.id2word is present, this is not needed. If both are provided, passed dictionary will be used.window_size (int, optional) – Is the size of the window to be used for coherence measures using boolean sliding window as their probability estimator. For ‘u_mass’ this doesn’t matter. If None  the default window sizes are used which are: ‘c_v’  110, ‘c_uci’  10, ‘c_npmi’  10.
coherence ({'u_mass', 'c_v', 'c_uci', 'c_npmi'}, optional) – Coherence measure to be used. Fastest method  ‘u_mass’, ‘c_uci’ also known as c_pmi. For ‘u_mass’ corpus should be provided, if texts is provided, it will be converted to corpus using the dictionary. For ‘c_v’, ‘c_uci’ and ‘c_npmi’ texts should be provided (corpus isn’t needed)
topn (int, optional) – Integer corresponding to the number of top words to be extracted from each topic.
processes (int, optional) – Number of processes to use for probability estimation phase, any value less than 1 will be interpreted as num_cpus  1.
 Returns
Each element in the list is a pair of a topic representation and its coherence score. Topic representations are distributions of words, represented as a list of pairs of word IDs and their probabilities.
 Return type
list of (list of (int, str), float)

update
(corpus, chunks_as_numpy=False)¶ Train the model with new documents, by EMiterating over corpus until the topics converge (or until the maximum number of allowed iterations is reached).
Train the model with new documents, by EMiterating over the corpus until the topics converge, or until the maximum number of allowed iterations is reached. corpus must be an iterable. The E step is distributed into the several processes.
Notes
This update also supports updating an already trained model (self) with new documents from corpus; the two models are then merged in proportion to the number of old vs. new documents. This feature is still experimental for nonstationary input streams.
For stationary input (no topic drift in new documents), on the other hand, this equals the online update of Hoffman et al. and is guaranteed to converge for any decay in (0.5, 1.0>.
 Parameters
corpus ({iterable of list of (int, float), scipy.sparse.csc}, optional) – Stream of document vectors or sparse matrix of shape (num_documents, num_terms) used to update the model.
chunks_as_numpy (bool) – Whether each chunk passed to the inference step should be a np.ndarray or not. Numpy can in some settings turn the term IDs into floats, these will be converted back into integers in inference, which incurs a performance hit. For distributed computing it may be desirable to keep the chunks as numpy.ndarray.

update_alpha
(gammat, rho)¶ Update parameters for the Dirichlet prior on the perdocument topic weights.
 Parameters
gammat (numpy.ndarray) – Previous topic weight parameters.
rho (float) – Learning rate.
 Returns
Sequence of alpha parameters.
 Return type
numpy.ndarray

update_eta
(lambdat, rho)¶ Update parameters for the Dirichlet prior on the pertopic word weights.
 Parameters
lambdat (numpy.ndarray) – Previous lambda parameters.
rho (float) – Learning rate.
 Returns
The updated eta parameters.
 Return type
numpy.ndarray

gensim.models.ldamulticore.
worker_e_step
(input_queue, result_queue, worker_lda)¶ Perform Estep for each job.
 Parameters
input_queue (queue of (int, list of (int, float),
Worker
)) – Each element is a job characterized by its ID, the corpus chunk to be processed in BOW format and the worker responsible for processing it.result_queue (queue of
LdaState
) – After the worker finished the job, the state of the resulting (trained) worker model is appended to this queue.worker_lda (
LdaMulticore
) – LDA instance which performed e step