Short Text Mining using Advanced Keras Layers and Maxent: shorttext 0.4.1

On 07/28/2017, shorttext published its release 0.4.1, with a few important updates. To install it, type the following in the OS X / Linux command line:

>>> pip install -U shorttext

The documentation in PythonHosted.org has been abandoned. It has been migrated to readthedocs.org. (URL: http://shorttext.readthedocs.io/ or http:// shorttext.rtfd.io)

Exploiting the Word-Embedding Layer

This update is mainly due to an important update in gensim, motivated by earlier shorttext‘s effort in integrating scikit-learn and keras. And gensim also provides a keras layer, on the same footing as other neural networks, activation function, or dropout layers, for Word2Vec models. Because shorttext has been making use of keras layers for categorization, such advance in gensim in fact makes it a natural step to add an embedding layer of all neural networks provided in shorttext. How to do it? (See shorttext tutorial for “Deep Neural Networks with Word Embedding.”)

import shorttext
wvmodel = shorttext.utils.load_word2vec_model('/path/to/GoogleNews-vectors-negative300.bin.gz')   # load the pre-trained Word2Vec model
trainclassdict = shorttext.data.subjectkeywords()   # load an example data set

 

To train a model, you can do it the old way, or do it the new way with additional gensim function:

kmodel = shorttext.classifiers.frameworks.CNNWordEmbed(wvmodel=wvmodel, nb_labels=len(trainclassdict.keys()), vecsize=100, with_gensim=True)   # keras model, setting with_gensim=True
classifier = shorttext.classifiers.VarNNEmbeddedVecClassifier(wvmodel, with_gensim=True, vecsize=100)   # instantiate the classifier, setting with_gensim=True
classifier.train(trainclassdict, kmodel)

The parameters with_gensim in both CNNWordEmbed and VarNNEmbeddedVecClassifier are set to be False by default, because of backward compatibility. However, setting it to be True will enable it to use the new gensim Word2Vec layer.

These change in gensim and shorttext are the works mainly contributed by Chinmaya Pancholi, a very bright student at Indian Institute of Technology, Kharagpur, and a GSoC (Google Summer of Code) student in 2017. He revolutionized gensim by integrating scikit-learn and keras into gensim. He also used what he did in gensim to improve the pipelines of shorttext. He provided valuable technical suggestions. You can read his GSoC proposal, and his blog posts in RaRe Technologies, Inc. Chinmaya has been diligently mentored by Ivan Menshikh and Lev Konstantinovskiy of RaRe Technologies.

Maxent Classifier

Another important update is the adding of maximum entropy (maxent) classifier. (See the corresponding tutorial on “Maximum Entropy (MaxEnt) Classifier.”) I will devote a separate entry on the theory, but it is very easy to use it,

import shorttext
from shorttext.classifiers import MaxEntClassifier

classifier = MaxEntClassifier()

Use the NIHReports dataset as the example:

classdict = shorttext.data.nihreports()
classifier.train(classdict, nb_epochs=1000)

The classification is just like other classifiers provided by shorttext:

classifier.score('cancer immunology') # NCI tops the score
classifier.score('children health') # NIAID tops the score
classifier.score('Alzheimer disease and aging') # NIAID tops the score

Continue reading “Short Text Mining using Advanced Keras Layers and Maxent: shorttext 0.4.1”

Advertisements

Release of shorttext 0.3.3

On November 21, 2016, the Python package `shorttext’ was published. Until today, more than seven versions have been published. There have been a drastic architecture change, but the overall purpose is still the same, as summarized in the first introduction entry:

This package `shorttext‘ was designed to tackle all these problems… It contains the following features:

  • example data provided (including subject keywords and NIH RePORT);
  • text preprocessing;
  • pre-trained word-embedding support;
  • gensim topic models (LDA, LSI, Random Projections) and autoencoder;
  • topic model representation supported for supervised learning using scikit-learn;
  • cosine distance classification; and
  • neural network classification (including ConvNet, and C-LSTM).

And since the first version, there have been updates, as summarized in the documention (News):

Version 0.3.3 (Apr 19, 2017)

  • Deleted CNNEmbedVecClassifier.
  • Added script ShortTextWord2VecSimilarity.

Version 0.3.2 (Mar 28, 2017)

  • Bug fixed for gensim model I/O;
  • Console scripts update;
  • Neural networks up to Keras 2 standard (refer to this).

Version 0.3.1 (Mar 14, 2017)

  • Compact model I/O: all models are in single files;
  • Implementation of stacked generalization using logistic regression.

Version 0.2.1 (Feb 23, 2017)

  • Removal attempts of loading GloVe model, as it can be run using gensim script;
  • Confirmed compatibility of the package with tensorflow;
  • Use of spacy for tokenization, instead of nltk;
  • Use of stemming for Porter stemmer, instead of nltk;
  • Removal of nltk dependencies;
  • Simplifying the directory and module structures;
  • Module packages updated.

Although there are still additions that I would love to add, but it would not change the overall architecture. I may add some more supervised learning algorithms, but under the same network. The upcoming big additions will be generative models or seq2seq models, but I do not see them coming in the short term. I will add corpuses.

I may add tutorials if I have time.

I am thankful that there is probably some external collaboration with other Python packages. Some people have already made some useful contributions. It will be updated if more things are confirmed.

Continue reading “Release of shorttext 0.3.3”

Author-Topic Models in gensim

Recently, gensim, a Python package for topic modeling, released a new version of its package which includes the implementation of author-topic models.

The most famous topic model is undoubtedly latent Dirichlet allocation (LDA), as proposed by David Blei and his colleagues. Such a topic model is a generative model, described by the following directed graphical models:

lda_pic

In the graph, \alpha and \beta are hyperparameters. \theta is the topic distribution of a document, z is the topic for each word in each document, \phi is the word distributions for each topic, and w is the generated word for a place in a document.

There are models similar to LDA, such as correlated topic models (CTM), where \phi is generated by not only \beta but also a covariance matrix \Sigma.

There exists an author model, which is a simpler topic model. The difference is that the words in the document are generated from the author for each document, as in the following graphical model. x is the author of a given word in the document.

author_pic

Combining these two, it gives the author-topic model as a hybrid, as shown below:

authortopic_pic

The new release of Python package, gensim, supported the author-topic model, as demonstrated in this Jupyter Notebook.

P.S.:

  • I am also aware that there is another topic model called structural topic model (STM), developed for the field of social science. However, there is no Python package supporting this, but an R package, called stm, is available for it. You can refer to their homepage too.
  • I may consider including author-topic model and STM in the next release of the Python package shorttext.

Continue reading “Author-Topic Models in gensim”

Python Package for Short Text Mining

There has been a lot of methods for natural language processing and text mining. However, in tweets, surveys, Facebook, or many online data, texts are short, lacking data to build enough information. Traditional bag-of-words (BOW) model gives sparse vector representation.

Semantic relations between words are important, because we usually do not have enough data to capture the similarity between words. We do not want “drive” and “drives,” or “driver” and “chauffeur” to be completely different.

The relation between or order of words become important as well. Or we want to capture the concepts that may be correlated in our training dataset.

We have to represent these texts in a special way and perform supervised learning with traditional machine learning algorithms or deep learning algorithms.

This package `shorttext‘ was designed to tackle all these problems. It is not a completely new invention, but putting everything known together. It contains the following features:

  • example data provided (including subject keywords and NIH RePORT);
  • text preprocessing;
  • pre-trained word-embedding support;
  • gensim topic models (LDA, LSI, Random Projections) and autoencoder;
  • topic model representation supported for supervised learning using scikit-learn;
  • cosine distance classification; and
  • neural network classification (including ConvNet, and C-LSTM).

Readers can refer this to the documentation.

Continue reading “Python Package for Short Text Mining”

Short Text Categorization using Deep Neural Networks and Word-Embedding Models

There are situations that we deal with short text, probably messy, without a lot of training data. In that case, we need external semantic information. Instead of using the conventional bag-of-words (BOW) model, we should employ word-embedding models, such as Word2Vec, GloVe etc.

Suppose we want to perform supervised learning, with three subjects, described by the following Python dictionary:

classdict={'mathematics': ['linear algebra',
           'topology',
           'algebra',
           'calculus',
           'variational calculus',
           'functional field',
           'real analysis',
           'complex analysis',
           'differential equation',
           'statistics',
           'statistical optimization',
           'probability',
           'stochastic calculus',
           'numerical analysis',
           'differential geometry'],
          'physics': ['renormalization',
           'classical mechanics',
           'quantum mechanics',
           'statistical mechanics',
           'functional field',
           'path integral',
           'quantum field theory',
           'electrodynamics',
           'condensed matter',
           'particle physics',
           'topological solitons',
           'astrophysics',
           'spontaneous symmetry breaking',
           'atomic molecular and optical physics',
           'quantum chaos'],
          'theology': ['divine providence',
           'soteriology',
           'anthropology',
           'pneumatology',
           'Christology',
           'Holy Trinity',
           'eschatology',
           'scripture',
           'ecclesiology',
           'predestination',
           'divine degree',
           'creedal confessionalism',
           'scholasticism',
           'prayer',
           'eucharist']}

And we implemented Word2Vec here. To add external information, we use a pre-trained Word2Vec model from Google, downloaded here. We can use it with Python package gensim. To load it, enter

from gensim.models import Word2Vec
wvmodel = Word2Vec.load_word2vec_format('<path-to>/GoogleNews-vectors-negative300.bin.gz', binary=True)

How do we represent a phrase in Word2Vec? How do we do the classification? Here I wrote two classes to do it.

Average

We can represent a sentence by summing the word-embedding representations of each word. The class, inside SumWord2VecClassification.py, is coded as follow:

from collections import defaultdict

import numpy as np
from nltk import word_tokenize
from scipy.spatial.distance import cosine

from utils import ModelNotTrainedException

class SumEmbeddedVecClassifier:
    def __init__(self, wvmodel, classdict, vecsize=300):
        self.wvmodel = wvmodel
        self.classdict = classdict
        self.vecsize = vecsize
        self.trained = False

    def train(self):
        self.addvec = defaultdict(lambda : np.zeros(self.vecsize))
        for classtype in self.classdict:
            for shorttext in self.classdict[classtype]:
                self.addvec[classtype] += self.shorttext_to_embedvec(shorttext)
            self.addvec[classtype] /= np.linalg.norm(self.addvec[classtype])
        self.addvec = dict(self.addvec)
        self.trained = True

    def shorttext_to_embedvec(self, shorttext):
        vec = np.zeros(self.vecsize)
        tokens = word_tokenize(shorttext)
        for token in tokens:
            if token in self.wvmodel:
                vec += self.wvmodel[token]
        norm = np.linalg.norm(vec)
        if norm!=0:
            vec /= np.linalg.norm(vec)
        return vec

    def score(self, shorttext):
        if not self.trained:
            raise ModelNotTrainedException()
        vec = self.shorttext_to_embedvec(shorttext)
        scoredict = {}
        for classtype in self.addvec:
            try:
                scoredict[classtype] = 1 - cosine(vec, self.addvec[classtype])
            except ValueError:
                scoredict[classtype] = np.nan
        return scoredict

Here the exception ModelNotTrainedException is just an exception raised if the model has not been trained yet, but scoring function was called by the user. (Codes listed in my Github repository.) The similarity will be calculated by cosine similarity.

Such an implementation is easy to understand and carry out. It is good enough for a lot of application. However, it has the problem that it does not take the relation between words or word order into account.

Convolutional Neural Network

To tackle the problem of word relations, we have to use deeper neural networks. Yoon Kim published a well cited paper regarding this in EMNLP in 2014, titled “Convolutional Neural Networks for Sentence Classification.” The model architecture is as follow: (taken from his paper)

cnn

Each word is represented by an embedded vector, but neighboring words are related through the convolutional matrix. And MaxPooling and a dense neural network were implemented afterwards. His paper involves multiple filters with variable window sizes / spatial extent, but for our cases of short phrases, I just use one window of size 2 (similar to dealing with bigram). While Kim implemented using Theano (see his Github repository), I implemented using keras with Theano backend. The codes, inside CNNEmbedVecClassification.py, are as follow:

import numpy as np
from keras.layers import Convolution1D, MaxPooling1D, Flatten, Dense
from keras.models import Sequential
from nltk import word_tokenize

from utils import ModelNotTrainedException

class CNNEmbeddedVecClassifier:
    def __init__(self,
                 wvmodel,
                 classdict,
                 n_gram,
                 vecsize=300,
                 nb_filters=1200,
                 maxlen=15):
        self.wvmodel = wvmodel
        self.classdict = classdict
        self.n_gram = n_gram
        self.vecsize = vecsize
        self.nb_filters = nb_filters
        self.maxlen = maxlen
        self.trained = False

    def convert_trainingdata_matrix(self):
        classlabels = self.classdict.keys()
        lblidx_dict = dict(zip(classlabels, range(len(classlabels))))

        # tokenize the words, and determine the word length
        phrases = []
        indices = []
        for label in classlabels:
            for shorttext in self.classdict[label]:
                category_bucket = [0]*len(classlabels)
                category_bucket[lblidx_dict[label]] = 1
                indices.append(category_bucket)
                phrases.append(word_tokenize(shorttext))

        # store embedded vectors
        train_embedvec = np.zeros(shape=(len(phrases), self.maxlen, self.vecsize))
        for i in range(len(phrases)):
            for j in range(min(self.maxlen, len(phrases[i]))):
                train_embedvec[i, j] = self.word_to_embedvec(phrases[i][j])
        indices = np.array(indices, dtype=np.int)

        return classlabels, train_embedvec, indices

    def train(self):
        # convert classdict to training input vectors
        self.classlabels, train_embedvec, indices = self.convert_trainingdata_matrix()

        # build the deep neural network model
        model = Sequential()
        model.add(Convolution1D(nb_filter=self.nb_filters,
                                filter_length=self.n_gram,
                                border_mode='valid',
                                activation='relu',
                                input_shape=(self.maxlen, self.vecsize)))
        model.add(MaxPooling1D(pool_length=self.maxlen-self.n_gram+1))
        model.add(Flatten())
        model.add(Dense(len(self.classlabels), activation='softmax'))
        model.compile(loss='categorical_crossentropy', optimizer='rmsprop')

        # train the model
        model.fit(train_embedvec, indices)

        # flag switch
        self.model = model
        self.trained = True

    def word_to_embedvec(self, word):
        return self.wvmodel[word] if word in self.wvmodel else np.zeros(self.vecsize)

    def shorttext_to_matrix(self, shorttext):
        tokens = word_tokenize(shorttext)
        matrix = np.zeros((self.maxlen, self.vecsize))
        for i in range(min(self.maxlen, len(tokens))):
            matrix[i] = self.word_to_embedvec(tokens[i])
        return matrix

    def score(self, shorttext):
        if not self.trained:
            raise ModelNotTrainedException()

        # retrieve vector
        matrix = np.array([self.shorttext_to_matrix(shorttext)])

        # classification using the neural network
        predictions = self.model.predict(matrix)

        # wrangle output result
        scoredict = {}
        for idx, classlabel in zip(range(len(self.classlabels)), self.classlabels):
            scoredict[classlabel] = predictions[0][idx]
        return scoredict

The output is a vector of length equal to the number of class labels, 3 in our example. The elements of the output vector add up to one, indicating its score, and a nature of probability.

Evaluation

A simple cross-validation to the example data set does not tell a difference between the two algorithms:

rplot_acc1

However, we can test the algorithm with a few examples:

Example 1: “renormalization”

  • Average: {‘mathematics’: 0.54135105096749336, ‘physics’: 0.63665460856632494, ‘theology’: 0.31014049736087901}
  • CNN: {‘mathematics’: 0.093827009201049805, ‘physics’: 0.85451591014862061, ‘theology’: 0.051657050848007202}

As renormalization was a strong word in the training data, it gives an easy result. CNN can distinguish much more clearly.

Example 2: “salvation”

  • Average: {‘mathematics’: 0.14939650156482298, ‘physics’: 0.21692765541184023, ‘theology’: 0.5698233329716329}
  • CNN: {‘mathematics’: 0.012395491823554039, ‘physics’: 0.022725773975253105, ‘theology’: 0.96487873792648315}

“Salvation” is not found in the training data, but it is closely related to “soteriology,” which means the doctrine of salvation. So it correctly identifies it with theology.

Example 3: “coffee”

  • Average: {‘mathematics’: 0.096820211601723272, ‘physics’: 0.081567332119268032, ‘theology’: 0.15962682945135631}
  • CNN: {‘mathematics’: 0.27321341633796692, ‘physics’: 0.1950736939907074, ‘theology’: 0.53171288967132568}

Coffee is not related to all subjects. The first architecture correctly indicates the fact, but CNN, with its probabilistic nature, has to roughly equally distribute it (but not so well.)

The code can be found in my Github repository: stephenhky/PyShortTextCategorization. (This repository has been updated since this article was published. The link shows the version of the code when this appeared online.)

Continue reading “Short Text Categorization using Deep Neural Networks and Word-Embedding Models”

Word Embedding Algorithms

Embedding has been hot in recent years partly due to the success of Word2Vec, (see demo in my previous entry) although the idea has been around in academia for more than a decade. The idea is to transform a vector of integers into continuous, or embedded, representations. Keras, a Python package that implements neural network models (including the ANN, RNN, CNN etc.) by wrapping Theano or TensorFlow, implemented it, as shown in the example below (which converts a vector of 200 features into a continuous vector of 10):

from keras.layers import Embedding
from keras.models import Sequential

# define and compile the embedding model
model = Sequential()
model.add(Embedding(200, 10, input_length=1))
model.compile('rmsprop', 'mse')  # optimizer: rmsprop; loss function: mean-squared error

We can then convert any features from 0 to 199 into vectors of 20, as shown below:

import numpy as np

model.predict(np.array([10, 90, 151]))

It outputs:

array([[[ 0.02915354,  0.03084954, -0.04160764, -0.01752155, -0.00056815,
         -0.02512387, -0.02073313, -0.01154278, -0.00389587, -0.04596512]],

       [[ 0.02981793, -0.02618774,  0.04137352, -0.04249889,  0.00456919,
          0.04393572,  0.04139435,  0.04415271,  0.02636364, -0.04997493]],

       [[ 0.00947296, -0.01643104, -0.03241419, -0.01145032,  0.03437041,
          0.00386361, -0.03124221, -0.03837727, -0.04804075, -0.01442516]]])

Of course, one must not omit a similar algorithm called GloVe, developed by the Stanford NLP group. Their codes have been wrapped in both Python (package called glove) and R (library called text2vec).

Besides Word2Vec, there are other word embedding algorithms that try to complement Word2Vec, although many of them are more computationally costly. Previously, I introduced LDA2Vec in my previous entry, an algorithm that combines the locality of words and their global distribution in the corpus. And in fact, word embedding algorithms with a similar ideas are also invented by other scientists, as I have introduced in another entry.

However, there are word embedding algorithms coming out. Since most English words carry more than a single sense, different senses of a word might be best represented by different embedded vectors. Incorporating word sense disambiguation, a method called sense2vec has been introduced by Trask, Michalak, and Liu. (arXiv:1511.06388). Matthew Honnibal wrote a nice blog entry demonstrating its use.

There are also other related work, such as wang2vec that is more sensitive to word orders.

Big Bang Theory (Season 2, Episode 5): Euclid Alternative

DMV staff: Application?
Sheldon: I’m actually more or a theorist.

Note: feature image taken from Big Bang Theory (CBS).

Continue reading “Word Embedding Algorithms”

Toying with Word2Vec

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 \text{puppy} - \text{dog} + \text{cat} by running

model.most_similar(positive=['puppy', 'cat'], negative=['dog'], topn=5)

This outputs:

[(u'kitten', 0.7634989619255066),
(u'puppies', 0.7110899686813354),
(u'pup', 0.6929495334625244),
(u'kittens', 0.6888389587402344),
(u'cats', 0.6796488761901855)]

which indicates that “kitten” is the answer (correctly!) The numbers are similarities of these words with the vector representation  \text{puppy} - \text{dog} + \text{cat} 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.

Mogu, my cat, three years ago when she was still a kitten
Mogu, my cat, three years ago when she was still a kitten

This demonstration shows that in the model, \text{puppy}-\text{dog} and \text{kitten}-\text{cat} 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:

model.most_similar(positive=['Beijing', 'Taiwan'], negative=['China'], topn=5)

which outputs

[(u'Taipei', 0.7866502404212952),
(u'Taiwanese', 0.6805002093315125),
(u'Kaohsiung', 0.6034111976623535),
(u'Chen', 0.5905819535255432),
(u'Seoul', 0.5865181684494019)]

Obviously, the answer is “Taipei.” And interestingly, the model sees Taiwan in the same footing of China!

Taipei (taken from Airasia: http://www.airasia.com/mo/en/destinations/taipei.page)

Past Participle of “eat”

We can extract grammatical information too. We know that the past participle of “go” is “gone”. With this, we can find that of “eat” by running:

model.most_similar(positive=[‘gone’, ‘eat’], negative=[‘go’], topn=5)

which outputs:

[(u'eaten', 0.7462186217308044),
(u'eating', 0.6516293287277222),
(u'ate', 0.6457351446151733),
(u'overeaten', 0.5853317975997925),
(u'eats', 0.5830586552619934)]

Capital of the State of Maryland

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:

model.most_similar(positive=['Sacramento', 'Maryland'], negative=['California'], topn=5)

which sadly outputs:

[(u'Towson', 0.7032245397567749),
(u'Baltimore', 0.6951349973678589),
(u'Hagerstown', 0.6367553472518921),
(u'Anne_Arundel', 0.5931429266929626),
(u'Oxon_Hill', 0.5879474878311157)]

But the correct answer should be Annapolis!

Downtown Annapolis (taken from Wikipedia)

Blue crabs (lunch in Cantler's Riverside Inn, Annapolis, MD)
Blue crabs (lunch in Cantler’s Riverside Inn, Annapolis, MD)

More About Word2Vec

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.

Continue reading “Toying with Word2Vec”

R or Python on Text Mining

rpythontextmining

I have seen more than enough debates about R or Python. While I do have a preference towards Python, I am happy with using R as well. I am not agnostic about languages, but we choose tools according to needs. The needs may be about effectiveness, efficiency, availability of tools, nature of problems, collaborations, etc. Yes, in a nutshell, it depends.

When dealing with text mining, although I still prefer Python, I have to fairly say that both languages have their own strengths and weaknesses. What do you do in text mining? Let me casually list the usual steps:

  1. Removing special characters,
  2. Removing numerals,
  3. Converting all alphabets to lower cases,
  4. Removing stop words, and
  5. Stemming the words (using Porter stemmer).

They are standard steps. But of course, sometimes we perform lemmatization instead of stemming. Sometimes we keep numerals. Or whatever. It is okay.

How do u do that in Python? Suppose you have a list of text documents stored in the variable texts, which is defined by

texts = ['I love Python.',
         'R is good for analytics.',
         'Mathematics is fun.']

. Then

# import all necessary libraries
from nltk.stem import PorterStemmer
from nltk.tokenize import SpaceTokenizer
from nltk.corpus import stopwords
from functools import partial
from gensim import corpora
from gensim.models import TfidfModel
import re

# initialize the instances for various NLP tools
tokenizer = SpaceTokenizer()
stemmer = PorterStemmer()

# define each steps
pipeline = [lambda s: re.sub('[^\w\s]', '', s),
            lambda s: re.sub('[\d]', '', s),
            lambda s: s.lower(),
            lambda s: ' '.join(filter(lambda s: not (s in stopwords.words()), tokenizer.tokenize(s))),
            lambda s: ' '.join(map(lambda t: stemmer.stem(t), tokenizer.tokenize(s)))
           ]

# function that carries out the pipeline step-by-step
def preprocess_text(text, pipeline):
    if len(pipeline)==0:
        return text
    else:
        return preprocess_text(pipeline[0](text), pipeline[1:])

# preprocessing
preprocessed_texts = map(partial(preprocess_text, pipeline=pipeline), texts)

# converting to feature vectors
documents = map(lambda s: tokenizer.tokenize(s), texts)
corpus = [dictionary.doc2bow(document) for document in documents]
tfidfmodel = TfidfModel(corpus)

We can train a classifier with the feature vectors output by tfidfmodel. To do the prediction, we can get the feature vector for a new text by calling:

bow = dictionary.doc2bow(tokenizer.tokenize(preprocess_text(text, pipeline)))

How about in R? To perform the preprocessing steps and extract the feature vectors, run:

library(RTextTools)
library(tm)

origmatrix<-create_matrix(textColumns = texts, language = 'english',
                          removeNumbers = TRUE, toLower = TRUE,
                          removeStopwords = 'TRUE', stemWords = TRUE,
                          weighting=tm::weightTfIdf, originalMatrix=NULL)

After we have a trained classifier, and we have a new text to preprocess, then we run:

matrix<-create_matrix(textColumns = newtexts, language = 'english',
                      removeNumbers = TRUE, toLower = TRUE,
                      removeStopwords = 'TRUE', stemWords = TRUE,
                      weighting=tm::weightTfIdf, originalMatrix=origmatrix)

Actually, from this illustration, a strength for R stands out: brevity. However, very often we want to preprocess in other ways, Python allows more flexibility without making it complicated. And Python syntax itself is intuitive enough.

And there are more natural language processing libraries in Python available, such as nltk and gensim, that are associated with its other libraries perfectly such as numpy, scipy and scikit-learn. But R is not far away in terms of this actually, as it has libraries such as tm and RTextTools, while R does not have numpy-like libraries because R itself is designed to perform calculations like this.

Python can be used to develop larger software projects by making the codes reusable, and it is obviously a weakness for R.

However, do perform analysis, R makes the task very efficient if we do not require something unconventional.

In the area of text mining, R or Python? My answer is: it depends.

Continue reading “R or Python on Text Mining”

Useful Python Packages

python
(Taken from http://latticeqcd.org/pythonorg/static/images/antigravity.png, adapted from http://xkcd.com/353/)

Python is the basic programming languages if one wants to work on data nowadays. Its popularity comes with its intuitive syntax, its support of several programming paradigms, and the package numpy (Numerical Python). Yes, if you asked which package is a “must-have” outside the standard Python packages, I would certainly name numpy.

Let me list some useful packages that I have found useful:

  1. numpy: Numerical Python. Its basic data type is ndarray, which acts like a vector with vectorized calculation support. It makes Python to perform matrix calculation efficiently like MATLAB and Octave. It supports a lot of commonly used linear algebraic algorithms, such as eigenvalue problems, SVD etc. It is the basic of a lot of other Python packages that perform heavy numerical computation. It is such an important package that, in some operating systems, numpy comes with Python as well.
  2. scipy: Scientific Python. It needs numpy, but it supports also sparse matrices, special functions, statistics, numerical integration…
  3. matplotlib: Graph plotting.
  4. scikit-learn: machine learning library. It contains a number of supervised and unsupervised learning algorithms.
  5. nltk: natural language processing. It provides not only basic tools like stemmers, lemmatizers, but also some algorithms like maximum entropy, tf-idf vectorizer etc. It provides a few corpuses, and supports WordNet dictionary.
  6. gensim: another useful natural language processing package with an emphasis on topic modeling. It mainly supports Word2Vec, latent semantic indexing (LSI), and latent Dirichlet allocation (LDA). It is convenient to construct term-document matrices, and convert them to matrices in numpy or scipy.
  7. networkx: a package that supports both undirected and directed graphs. It provides basic algorithms used in graphs.
  8. sympy: Symbolic Python. I am not good at this package, but I know mathics and SageMath are both based on it.
  9. pandas: it supports data frame handling like R. (I have not used this package as I am a heavy R user.)

Of course, if you are a numerical developer, to save you a good life, install Anaconda.

There are some other packages that are useful, such as PyCluster (clustering), xlrd (Excel files read/write), PyGame (writing games)… But since I have not used them, I would rather mention it in this last paragraph, not to endorse but avoid devaluing it.

Don’t forget to type in your IPython Notebook:

import antigravity

Continue reading “Useful Python Packages”

Blog at WordPress.com.

Up ↑