`models.ldamodel` – Latent Dirichlet Allocation¶

Optimized Latent Dirichlet Allocation (LDA) in Python.

For a faster implementation of LDA (parallelized for multicore machines), see also gensim.models.ldamulticore.

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 Matthew D. Hoffman, David M. Blei, Francis Bach: ‘Online Learning for Latent Dirichlet Allocation’, NIPS 2010.

The 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.
Is distributed: makes use of a cluster of machines, if available, to speed up model estimation.

Usage examples¶

Train an LDA model using a Gensim corpus

>>> from gensim.test.utils import common_texts
>>> from gensim.corpora.dictionary import Dictionary
>>>
>>> # Create a corpus from a list of texts
>>> common_dictionary = Dictionary(common_texts)
>>> common_corpus = [common_dictionary.doc2bow(text) for text in common_texts]
>>>
>>> # Train the model on the corpus.
>>> lda = LdaModel(common_corpus, num_topics=10)

Save a model to disk, or reload a pre-trained 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, the model using new, unseen documents

>>> # Create a new corpus, made of previously 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)
>>> vector = lda[unseen_doc]

A lot of parameters can be tuned to optimize training for your specific case

>>> lda = LdaModel(common_corpus, num_topics=50, alpha='auto', eval_every=5)  # learn asymmetric alpha from data

class gensim.models.ldamodel.LdaModel(corpus=None, num_topics=100, id2word=None, distributed=False, chunksize=2000, passes=1, update_every=1, alpha='symmetric', eta=None, decay=0.5, offset=1.0, eval_every=10, iterations=50, gamma_threshold=0.001, minimum_probability=0.01, random_state=None, ns_conf=None, minimum_phi_value=0.01, per_word_topics=False, callbacks=None, dtype=<class 'numpy.float32'>)¶

Bases: TransformationABC, BaseTopicModel

Train and use Online Latent Dirichlet Allocation model as presented in ‘Online Learning for LDA’ by Hoffman et al.

Examples

Initialize a model using a Gensim corpus

>>> from gensim.test.utils import common_corpus
>>>
>>> lda = LdaModel(common_corpus, num_topics=10)

You can then infer topic distributions on new, unseen documents.

>>> doc_bow = [(1, 0.3), (2, 0.1), (0, 0.09)]
>>> doc_lda = lda[doc_bow]

The model can be updated (trained) with new documents.

>>> # In practice (corpus =/= initial training corpus), but we use the same here for simplicity.
>>> other_corpus = common_corpus
>>>
>>> lda.update(other_corpus)

Model persistency is achieved through load() and save() methods.

Parameters

corpus (iterable of list of (int, float), optional) – Stream of document vectors or sparse matrix of shape (num_documents, num_terms). If you have a CSC in-memory matrix, you can convert it to a streamed corpus with the help of gensim.matutils.Sparse2Corpus. 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.
distributed (bool, optional) – Whether distributed computing should be used to accelerate training.
chunksize (int, optional) – Number of documents to be used in each training chunk.
passes (int, optional) – Number of passes through the corpus during training.
update_every (int, optional) – Number of documents to be iterated through for each update. Set to 0 for batch learning, > 1 for online iterative learning.
alpha ({float, numpy.ndarray of float, list of float, str}, optional) –
A-priori belief on document-topic distribution, this can be:
- scalar for a symmetric prior over document-topic distribution,
- 1D array of length equal to num_topics to denote an asymmetric user defined prior for each topic.
Alternatively default prior selecting strategies can be employed by supplying a string:
- ’symmetric’: (default) Uses a fixed symmetric prior of 1.0 / num_topics,
- ’asymmetric’: Uses a fixed normalized asymmetric prior of 1.0 / (topic_index + sqrt(num_topics)),
- ’auto’: Learns an asymmetric prior from the corpus (not available if distributed==True).
eta ({float, numpy.ndarray of float, list of float, str}, optional) –
A-priori belief on topic-word distribution, this can be:
- scalar for a symmetric prior over topic-word distribution,
- 1D array of length equal to num_words to denote an asymmetric user defined prior for each word,
- matrix of shape (num_topics, num_words) to assign a probability for each word-topic combination.
Alternatively default prior selecting strategies can be employed by supplying a string:
- ’symmetric’: (default) Uses a fixed symmetric prior of 1.0 / num_topics,
- ’auto’: Learns an asymmetric prior from the corpus.
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 ‘Online Learning for LDA’ by Hoffman et al.
offset (float, optional) – Hyper-parameter that controls how much we will slow down the first steps the first few iterations. Corresponds to $\tau_0$ from ‘Online Learning for LDA’ by Hoffman et al.
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.
ns_conf (dict of (str, object), optional) – Key word parameters propagated to gensim.utils.getNS() to get a Pyro4 nameserver. Only used if distributed is set to True.
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).
callbacks (list of Callback) – Metric callbacks to log and visualize evaluation metrics of the model during training.
dtype ({numpy.float16, numpy.float32, numpy.float64}, optional) – Data-type to use during calculations inside model. All inputs are also converted.

__getitem__(bow, eps=None)¶

Get the topic distribution for the given document.

Wraps get_document_topics() to support an operator style call. Uses the model’s current state (set using constructor arguments) to fill in the additional arguments of the wrapper method.

Parameters

bow (list of (int, float)) – The document in BOW format.
eps (float, optional) – Topics with an assigned probability lower than this threshold will be discarded.

Returns

Topic distribution for the given document. Each topic is represented as a pair of its ID and the probability assigned to it.

Return type

list of (int, float)

add_lifecycle_event(event_name, log_level=20, **event)¶

Append an event into the lifecycle_events attribute of this object, and also optionally log the event at log_level.

Events are important moments during the object’s life, such as “model created”, “model saved”, “model loaded”, etc.

The lifecycle_events attribute is persisted across object’s save() and load() operations. It has no impact on the use of the model, but is useful during debugging and support.

Set self.lifecycle_events = None to disable this behaviour. Calls to add_lifecycle_event() will not record events into self.lifecycle_events then.

Parameters

event_name (str) – Name of the event. Can be any label, e.g. “created”, “stored” etc.
event (dict) –
Key-value mapping to append to self.lifecycle_events. Should be JSON-serializable, so keep it simple. Can be empty.

This method will automatically add the following key-values to event, so you don’t have to specify them:
- datetime: the current date & time
- gensim: the current Gensim version
- python: the current Python version
- platform: the current platform
- event: the name of this event
log_level (int) – Also log the complete event dict, at the specified log level. Set to False to not log at all.

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 1e-8 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 word-topic 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 term-topic 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 non-negative 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 topic-word 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 ({float, numpy.ndarray of float, list of float, str}) –
A-priori belief on document-topic distribution. If name == ‘alpha’, then the prior can be:
- scalar for a symmetric prior over document-topic distribution,
- 1D array of length equal to num_topics to denote an asymmetric user defined prior for each topic.
Alternatively default prior selecting strategies can be employed by supplying a string:
- ’symmetric’: (default) Uses a fixed symmetric prior of 1.0 / num_topics,
- ’asymmetric’: Uses a fixed normalized asymmetric prior of 1.0 / (topic_index + sqrt(num_topics)),
- ’auto’: Learns an asymmetric prior from the corpus (not available if distributed==True).
A-priori belief on topic-word distribution. If name == ‘eta’ then the prior can be:
- scalar for a symmetric prior over topic-word distribution,
- 1D array of length equal to num_words to denote an asymmetric user defined prior for each word,
- matrix of shape (num_topics, num_words) to assign a probability for each word-topic combination.
Alternatively default prior selecting strategies can be employed by supplying a string:
- ’symmetric’: (default) Uses a fixed symmetric prior of 1.0 / 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).

Returns

init_prior (numpy.ndarray) – Initialized Dirichlet prior: If ‘alpha’ was provided as name the shape is (self.num_topics, ). If ‘eta’ was provided as name the shape is (len(self.id2word), ).
is_auto (bool) – Flag that shows if hyperparameter optimization should be used or not.

classmethod load(fname, *args, **kwargs)¶

Load a previously saved gensim.models.ldamodel.LdaModel from file.

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models.ldamodel – Latent Dirichlet Allocation¶

Usage examples¶

`models.ldamodel` – Latent Dirichlet Allocation¶