A New Document Embedding Method for News Classification

Text classification is one of the main tasks of natural language processing (NLP). In this task, documents are classified into pre-defined categories. There is lots of news spreading on the web. A text classifier can categorize news automatically and this facilitates and accelerates access to the news. The first step in text classification is to represent documents in a suitable way that can be distinguishable by a classifier. There is an abundance of methods in the literature for document representation which can be divided into a bag of words model, graph-based methods, word embedding pooling, neural network-based, and topic modeling based methods. Most of these methods only use local word co-occurrences to generate document embeddings. Local word co-occurrences miss the overall view of a document and topical information which can be very useful for classifying news articles.  In this paper, we propose a method that utilizes term-document and document-topic matrix to generate richer representations for documents.  Term-document matrix represents a document in a specific way where each word plays a role in representing a document. The generalization power of this type of representation for text classification and information retrieval is not very well. This matrix is created based on global co-occurrences (in document-level). These types of co-occurrences are more suitable for text classification than local co-occurrences. Document-topic matrix represents a document in an abstract way and the higher level co-occurrences are used to generate this matrix. So this type of representation has a good generalization power for text classification but it is so high-level and misses the rare words as features which can be very useful for text classification. The proposed approach is an unsupervised document-embedding model that utilizes the benefit of both document-topic and term-document matrices to generate a richer representation for documents. This method constructs a tensor with the help of these two matrices and applied tensor factorization to reveal the hidden aspects of data. The proposed method is evaluated on the task of text classification on 20-Newsgroups and R8 datasets which are benchmark datasets in the news classification area. The results show the superiority of the proposed model with respect to baseline methods. The accuracy of text classification is improved by 3%.