1. A computer-implemented method for sentiment analysis from social media content, comprising: performing by at least one processor the steps of: crawling a plurality of websites to obtain metadata from social media content; extracting the metadata from the social media content by identifying at least one sentiment-bearing keyword and a polarity thereof in a sentence from the social media content; determining at least one category corresponding to the at least one sentiment-bearing keyword of the sentence; and determining at least one sentiment corresponding to the at least one category based on the at least one sentiment-bearing keyword, wherein, the method comprises the step of extracting a list of keywords from a plurality of documents, the step of extracting the list of keywords including: (a) extracting keywords from each document of the plurality of documents, and for each keyword, (b) for each keyword, calculating a frequency, f, of the keyword in the plurality of documents and a number of documents, N, that include the keyword, using a phase transition formula to calculate a relevancy of the keyword based on the frequency of the keyword in the plurality of documents and the number of documents that include the keyword, and adding the keyword to the list of keywords when the relevancy of the keyword exceeds a predetermined threshold.