ELM-Based Active Learning via Asymmetric Samplers: Constructing a Multi-Class Text Corpus for Emotion Classification

A high-quality annotated text corpus is vital when training a deep learning model. However, it is insurmountable to acquire absolute abundant label-balanced data because of the huge labor and time costs needed in the labeling stage. To alleviate this situation, a novel active learning (AL) method is proposed in this paper, which is designed to scratch samples to construct multi-class and multi-label Chinese emotional text corpora. This work shrewdly leverages the superiorities, i.e., less learning time and generating parameters randomly possessed by extreme learning machines (ELMs), to initially measure textual emotion features. In addition, we designed a novel combined query strategy called an asymmetric sampler (which simultaneously considers uncertainty and representativeness) to verify and extract ideal samples. Furthermore, this model progressively modulates state-of-the-art prescriptions through cross-entropy, Kullback–Leibler, and Earth Mover’s distance. Finally, through stepwise-assessing the experimental results, the updated corpora present more enriched label distributions and have a higher weight of correlative emotional information. Likewise, in emotion classification experiments by ELM, the precision, recall, and F1 scores obtained 7.17%, 6.31%, and 6.71% improvements, respectively. Extensive emotion classification experiments were conducted by two widely used classifiers—SVM and LR—and their results also prove our method’s effectiveness in scratch emotional texts through comparisons.