How to use Gensim doc2vec with pre-trained word vectors?

Note that the "DBOW" (dm=0) training mode doesn't require or even create word-vectors as part of the training. It merely learns document vectors that are good at predicting each word in turn (much like the word2vec skip-gram training mode).

(Before gensim 0.12.0, there was the parameter train_words mentioned in another comment, which some documentation suggested will co-train words. However, I don't believe this ever actually worked. Starting in gensim 0.12.0, there is the parameter dbow_words, which works to skip-gram train words simultaneous with DBOW doc-vectors. Note that this makes training take longer – by a factor related to window. So if you don't need word-vectors, you may still leave this off.)

In the "DM" training method (dm=1), word-vectors are inherently trained during the process along with doc-vectors, and are likely to also affect the quality of the doc-vectors. It's theoretically possible to pre-initialize the word-vectors from prior data. But I don't know any strong theoretical or experimental reason to be confident this would improve the doc-vectors.

One fragmentary experiment I ran along these lines suggested the doc-vector training got off to a faster start – better predictive qualities after the first few passes – but this advantage faded with more passes. Whether you hold the word vectors constant or let them continue to adjust with the new training is also likely an important consideration... but which choice is better may depend on your goals, data set, and the quality/relevance of the pre-existing word-vectors.

(You could repeat my experiment with the intersect_word2vec_format() method available in gensim 0.12.0, and try different levels of making pre-loaded vectors resistant-to-new-training via the syn0_lockf values. But remember this is experimental territory: the basic doc2vec results don't rely on, or even necessarily improve with, reused word vectors.)

Well, I am recently using Doc2Vec too. And I was thinking of using LDA result as word vector and fix those word vectors to get a document vector. The result isn't very interesting though. Maybe it's just my data set isn't that good. The code is below. Doc2Vec saves word vectors and document vectors together in dictionary doc2vecmodel.syn0. You can direct change the vector values. The only problem may be that you need to find out which position in syn0 represents which word or document. The vectors are stored in random order in dictionary syn0.

import logginglogging.basicConfig(format='%(asctime)s : %(levelname)s : %(message)s', level=logging.INFO)from gensim import corpora, models, similaritiesimport gensimfrom sklearn import svm, metricsimport numpy#Read in texts into div_texts(for LDA and Doc2Vec)div_texts = []f = open("clean_ad_nonad.txt")lines = f.readlines()f.close()for line in lines:    div_texts.append(line.strip().split(" "))#Set up dictionary and MMcorpusdictionary = corpora.Dictionary(div_texts)dictionary.save("ad_nonad_lda_deeplearning.dict")#dictionary = corpora.Dictionary.load("ad_nonad_lda_deeplearning.dict")print dictionary.token2id["junk"]corpus = [dictionary.doc2bow(text) for text in div_texts]corpora.MmCorpus.serialize("ad_nonad_lda_deeplearning.mm", corpus)#LDA trainingid2token = {}token2id = dictionary.token2idfor onemap in dictionary.token2id:    id2token[token2id[onemap]] = onemap#ldamodel = models.LdaModel(corpus, num_topics = 100, passes = 1000, id2word = id2token)#ldamodel.save("ldamodel1000pass.lda")#ldamodel = models.LdaModel(corpus, num_topics = 100, id2word = id2token)ldamodel = models.LdaModel.load("ldamodel1000pass.lda")ldatopics = ldamodel.show_topics(num_topics = 100, num_words = len(dictionary), formatted = False)print ldatopics[10][1]print ldatopics[10][1][1]ldawordindex = {}for i in range(len(dictionary)):    ldawordindex[ldatopics[0][i][1]] = i#Doc2Vec initializesentences = []for i in range(len(div_texts)):    string = "SENT_" + str(i)    sentence = models.doc2vec.LabeledSentence(div_texts[i], labels = [string])    sentences.append(sentence)doc2vecmodel = models.Doc2Vec(sentences, size = 100, window = 5, min_count = 0, dm = 1)print "Initial word vector for word junk:"print doc2vecmodel["junk"]#Replace the word vector with word vectors from LDAprint len(doc2vecmodel.syn0)index2wordcollection = doc2vecmodel.index2wordprint index2wordcollectionfor i in range(len(doc2vecmodel.syn0)):    if index2wordcollection[i].startswith("SENT_"):        continue    wordindex = ldawordindex[index2wordcollection[i]]    wordvectorfromlda = [ldatopics[j][wordindex][0] for j in range(100)]    doc2vecmodel.syn0[i] = wordvectorfromlda#print doc2vecmodel.index2word[26841]#doc2vecmodel.syn0[0] = [0 for i in range(100)]print "Changed word vector for word junk:"print doc2vecmodel["junk"]#Train Doc2Vecdoc2vecmodel.train_words = False print "Initial doc vector for 1st document"print doc2vecmodel["SENT_0"]for i in range(50):    print "Round: " + str(i)    doc2vecmodel.train(sentences)print "Trained doc vector for 1st document"print doc2vecmodel["SENT_0"]#Using SVM to do classificationresultlist = []for i in range(4143):    string = "SENT_" + str(i)    resultlist.append(doc2vecmodel[string])svm_x_train = []for i in range(1000):    svm_x_train.append(resultlist[i])for i in range(2210,3210):    svm_x_train.append(resultlist[i])print len(svm_x_train)svm_x_test = []for i in range(1000,2210):    svm_x_test.append(resultlist[i])for i in range(3210,4143):    svm_x_test.append(resultlist[i])print len(svm_x_test)svm_y_train = numpy.array([0 for i in range(2000)])for i in range(1000,2000):    svm_y_train[i] = 1print svm_y_trainsvm_y_test = numpy.array([0 for i in range(2143)])for i in range(1210,2143):    svm_y_test[i] = 1print svm_y_testsvc = svm.SVC(kernel='linear')svc.fit(svm_x_train, svm_y_train)expected = svm_y_testpredicted = svc.predict(svm_x_test)print("Classification report for classifier %s:\n%s\n"      % (svc, metrics.classification_report(expected, predicted)))print("Confusion matrix:\n%s" % metrics.confusion_matrix(expected, predicted))print doc2vecmodel["junk"]

This forked version of gensim allows loading pre-trained word vectors for training doc2vec. Here you have an example on how to use it. The word vectors must be in the C-word2vec tool text format: one line per word vector where first comes a string representing the word and then space-separated float values, one for each dimension of the embedding.

This work belongs to a paper in which they claim that using pre-trained word embeddings actually helps building the document vectors. However I am getting almost the same results no matter I load the pre-trained embeddings or not.

Edit: actually there is one remarkable difference in my experiments. When I loaded the pretrained embeddings I trained doc2vec for half of the iterations to get almost the same results (training longer than that produced worse results in my task).