Sentiment analysis is one of the prominent research areas in data mining and knowledge discovery, which has proven to be an effective technique for monitoring public opinion. The big data era with a high volume of data generated by a variety of sources has provided enhanced opportunities for utilizing sentiment analysis in various domains. In order to take best advantage of the high volume of data for accurate sentiment analysis, it is essential to clean the data before the analysis, as irrelevant or redundant data will hinder extracting valuable information. In this paper, we propose a hybrid feature selection algorithm to improve the performance of sentiment analysis tasks. Our proposed sentiment analysis approach builds a binary classification model based on two feature selection techniques: an entropy-based metric and an evolutionary algorithm. We have performed comprehensive experiments in two different domains using a benchmark dataset, Stanford Sentiment Treebank, and a real-world dataset we have created based on World Health Organization (WHO) public speeches regarding COVID-19. The proposed feature selection model is shown to achieve significant performance improvements in both datasets, increasing classification accuracy for all utilized machine learning and text representation technique combinations. Moreover, it achieves over 70% reduction in feature size, which provides efficiency in computation time and space.

Natural Language Processing (NLP) is a prominent subject which includes various subcategories such as text classification, error correction, machine translation, etc. Unlike other languages, there are limited number of Turkish NLP studies in literature. In this study, we apply text classification on Turkish documents by using n-gram features. Our algorithm applies different preprocessing techniques, namely, n-gram choice (character level or word level, bigram or trigram models), stemming, and use of punctuation, and then determines the Turkish document's author and genre, and the gender of the author. For this purpose, Naive Bayes, Support Vector Machines and Random Forest are used as classification techniques. Finally, we discuss the effects of above mentioned preprocessing techniques to the performance of Turkish text classification.