Using a github code for my journal paper I'm conducting research on cyber bullying classification. I recently found a github repository containing code on sentiment analysis which looked at different machine learning algorithms, doc2vec + ml classifiers and a word2vec + cnn model. My dataset is different and I do use different machine learning classifiers than the github code does. However, the way the code in the repository trained the cnn model and the word2vec that was used is exactly the same.
Would using the code in the repository for my problem be considered plagiarism?
It would be plagiarism only if you don't cite the source. There's no plagiarism issue if you properly explain that you use this source code as a basis for your implementation and make it clear that it's not yours (preferably by citing a paper from the original authors if any, if not just give the github link).
Whether this will be considered an original contribution by the reviewers is a different matter. It might be ok if your motivation and data are significantly different from what the original authors did.