4. The computer-implemented method of claim 3 further comprising: adding, to the data structure, the unseen n-grams.
3. The computer-implemented method of claim 1 , wherein identifying the unseen n-grams includes: comparing n-grams of the corresponding data snippet with n-grams in a data structure storing seen n-grams, wherein seen n-grams are n-grams that have occurred in one or more of the data snippets processed prior to the corresponding data snippet, and identifying those of the n-grams of the corresponding data snippet that do not match with the seen n-grams as the unseen n-grams.