In these few days, Facebook published a new research paper, regarding the use of sequence to sequence (seq2seq) model for machine translation. What is special about this seq2seq model is that it uses convolutional neural networks (ConvNet, or CNN), instead of recurrent neural networks (RNN).
The original seq2seq model is implemented with Long Short-Term Memory (LSTM) model, published by Google.(see their paper) It is basically a character-based model that generates texts according to a sequence of input characters. And the same author constructed a neural conversational model, (see their paper) as mentioned in a previous blog post. Daewoo Chong, from Booz Allen Hamilton, presented its implementation using Tensorflow in DC Data Education Meetup on April 13, 2017. Johns Hopkins also published a spell correction algorithm implemented in seq2seq. (see their paper) The real advantage of RNN over CNN is that there is no limit about the size of the tokens input or output.
While the fixing of the size of vectors for CNN is obvious, using CNN serves the purpose of limiting the size of input vectors, and thus limiting the size of contexts. This limits the contents, and speeds up the training process. RNN is known to be trained slow. Facebook uses this CNN seq2seq model for their machine translation model. For more details, take a look at their paper and their Github repository.
Previously, I wrote an entry on text mining on R and Python, and did a comparison. However, the text mining package employed was tm for R. But it has some problems:
The syntax is not natural for an experienced R users.
tm uses simple_triplet_matrix from the slam library for document-term matrix (DTM) and term-occurrence matrix (TCM), which is not as widely used as dgCMatrix from the Matrix library.
Tommy Jones, a Ph.D. student in George Mason University, and a data scientist at Impact Research, developed an alternative text mining package called textmineR. He presented in a Stat Prog DC Meetup on April 27, 2016. It employed a better syntax, and dgCMatrix. All in all, it is a wrapper for a lot of existing R packages to facilitate the text mining process, like creating DTM matrices with stopwords or appropriate stemming/lemmatizing functions. Here is a sample code to create a DTM with the example from the previous entry:
texts <- c('I love Python.',
'R is good for analytics.',
'Mathematics is fun.')
doc_names = c(1:length(texts)),
ngram_window = c(1, 1),
stopword_vec = c(tm::stopwords('english'), tm::stopwords('SMART')),
lower = TRUE,
remove_punctuation = TRUE,
remove_numbers = TRUE
The DTM is a sparse matrix:
3 x 6 sparse Matrix of class &quot;dgCMatrix&quot;
analytics fun mathematics good python love
1 . . . . 1 1
2 1 . . 1 . .
3 . 1 1 . . .
On the other hand, it wraps text2vec, an R package that wraps the word-embedding algorithm named gloVe. And it wraps a number of topic modeling algorithms, such as latent Dirichlet allocation (LDA) and correlated topic models (CTM).
In addition, it contains a parallel computing loop function called TmParallelApply, analogous to the original R parallel loop function mclapply, but TmParallelApply works on Windows as well.
textmineR is an open-source project, with source code available on github, which contains his example codes.
We “sensed” what has been the current hot issues in the past (and we still often do today.) Methods of “sensing,” or “detecting”, is now more sophisticated however as the computational technologies are now more advanced. The methods involved can be collected to a field called “computational journalism.”
Recently, there is a blog post by Jeiran about understanding the public impression about Iran using computational methods. She divided the question into the temporal and topical perspectives. The temporal perspective is about various time-varying patterns of the number of related news articles; the topical perspective is about the distribution of various topics, using latent Dirichlet allocation (LDA), and Bayes’ Theorem. The blog post is worth reading.
In February last year, there was a video clip online that Daeil Kim, a data scientist at New York Times, spoke at NYC Data Science Meetup. Honestly, I still have not watched it yet (but I think I should have.) What his work is also about computational journalism, on his algorithm, and LDA.
Of course, computational journalism is the application of natural language processing and machine learning on news articles… However, as a computational physicist has to know physics, a computational journalist has to know journalism. A data scientist has to be someone who knows the technology and the subject matter.
It is another task of text mining and natural language processing. He mentioned a few common tools. However, he also specifically looked at rhymes (as rhyme is an important element of rap lyrics), and profanity (as rap music is commonly, or stereotypically, dirty).
One fascinating application of deep learning is the training of a model that outputs vectors representing words. A project written in Google, named Word2Vec, is one of the best tools regarding this. The vector representation captures the word contexts and relationships among words. This tool has been changing the landscape of natural language processing (NLP).
Let’s have some demonstration. To use Word2Vec in Python, you need to have the package gensim installed. (Installation instruction: here) And you have to download a trained model (GoogleNews-vectors-negative300.bin.gz), which is 3.6 GB big!! When you get into a Python shell (e.g., IPython), type
from gensim.models.word2vec import Word2Vec
model = Word2Vec.load_word2vec_format('GoogleNews-vectors-negative300.bin', binary=True)
This model enables the user to extract vector representation of length 300 of an English word. So what is so special about this vector representation from the traditional bag-of-words representation? First, the representation is standard. Once trained, we can use it in future training or testing dataset. Second, it captures the context of the word in a way that the algebraic operation of these vectors has meanings.
Here I give 5 examples.
A Juvenile Cat
What is a juvenile cat? We know that a juvenile dog is a puppy. Then we can get it by carry out the algebraic calculation by running
which indicates that “kitten” is the answer (correctly!) The numbers are similarities of these words with the vector representation in descending order. You can verify it by calculating the cosine distance:
from scipy.spatial import distance
print (1-distance.cosine(model['kitten'], model['puppy']+model['cat']-model['dog']))
which outputs 0.763498957413.
This demonstration shows that in the model, and are of similar semantic relations.
Capital of Taiwan
Where is the capital of Taiwan? We can find it if we know the capital of another country. For example, we know that Beijing is the capital of China. Then we can run the following:
However, this model does not always work. If it can find the capital of Taiwan, can it find those for any states in the United States? We know that the capital of California is Sacramento. How about Maryland? Let’s run:
Word2Vec was developed by Tomáš Mikolov. He previously worked for Microsoft Research. However, he switched to Google, and published a few influential works on Word2Vec. [Mikolov, Yih, Zweig 2013] [Mikolov, Sutskever, Chen, Corrado, Dean 2013] [Mikolov, Chen, Corrado, Dean 2013] Their conference paper in 2013 can be found on arXiv. He later published a follow-up work on a package called Doc2Vec that considers phrases. [Le, Mikolov 2014]
Earlier this year, I listened to a talk in DCNLP meetup spoken by Michael Czerny on his award-winning blog entry titled “Modern Methods for Sentiment Analysis.” He applied the vector representations of words by Word2Vec to perform sentiment analysis, assuming that similar sentiments cluster together in the vector space. (He took averages of the vectors in tweets to extract emotions.) [Czerny 2015] I highly recommend you to read his blog entry. On the other hand, Xin Rong wrote an explanation about how Word2Vec works too. [Rong 2014]
There seems to be no progress on the project Word2Vec anymore as Tomáš Mikolov no longer works in Google. However, the Stanford NLP Group recognized that Word2Vec captures the relations between words in their vector representation. They worked on a similar project, called GloVe (Global Vectors), which tackles the problem with matrix factorization. [Pennington, Socher, Manning 2014] Radim Řehůřek did some analysis comparing Word2Vec and GloVe. [Řehůřek 2014] GloVe can be implemented in Python too.
On October 14, 2015, I attended the regular meeting of the DCNLP meetup group, a group on natural language processing (NLP) in Washington, DC area. The talk was titled “Deep Learning for Question Answering“, spoken by Mr. Mohit Iyyer, a Ph.D. student in Department of Computer Science, University of Maryland (my alma mater!). He is a very good speaker.
I have no experience on deep learning at all although I did write a blog post remotely related. I even didn’t start training my first neural network until the next day after the talk. However, Mr. Iyyer explained what recurrent neural network (RNN), recursive neural network, and deep averaging network (DAN) are. This helped me a lot in order to understanding more about the principles of the famous word2vec model (which is something I am going to write about soon!). You can refer to his slides for more details. There are really a lot of talents in College Park, like another expert, Joe Yue Hei Ng, who is exploiting deep learning a lot as well.
The applications are awesome: with external knowledge to factual question answering, reasoning-based question answering, and visual question answering, with increasing order of challenging levels.
Mr. Iyyer and the participants discussed a lot about different packages. Mr. Iyyer uses Theano, a Python package for deep learning, which is good for model building and other analytical work. Some prefer Caffe. Some people, who are Java developers, also use deeplearning4j.
This meetup was a sacred one too, because it is the last time it was held in Stetsons Famous Bar & Grill at U Street, which is going to permanently close on Halloween this year. The group is eagerly looking for a new venue for the upcoming meetup. This meeting was a crowded one. I sincerely thank the organizers, Charlie Greenbacker and Liz Merkhofer, for hosting all these meetings, and Chris Phipps (a linguist from IBM Watson) for recording.
I heard about this project, EMBERS (acronym to Early Model Based Event Recognition using Surrogates), in a DC Data Science meetup. The speaker was Naren Ramakrishnan from VirginiaTech.
To me, it is a real big data project. It is a software that forecasts massive atrocities, particularly on civil unrest (mainly in Latin America and Middle East). They make use of open-source indicators, such as tweets, Facebook events, news, blog posts, open economic figures etc. to predict the outbreak of big events with advanced mathematical models. It is collaborative project involves nine universities and private corporations.
EMBERS ingests a large amount of unstructured data 24/7. Evidently, techniques in natural language processing (NLP) are involved. Besides English, at least Spanish and Arabic are incorporated into the system. And this real-time prediction process is very challenging.
The system performance is quite good. For a 24-month period, it has a recall of 0.65 and a precision of 0.94.
Who need EMBERS? Government must be a big customer. And not surprisingly, some travelers, social scientists and corporate firms find it useful because safety in, information about and business environment in various countries are their main concerns. Of course it is not a free software. It is undeniably a lucrative project.
One of the many protests against the 2014 World Cup in Sao Paulo, May 15, 2014.NACHO DOCE/REUTERS