GitHub user gczsjdy opened a pull request: https://github.com/apache/spark/pull/17359
Add aggreagate expression nGrams ## What changes were proposed in this pull request? This is the implementation of Hive's `ngrams`, which is a popular statistical and data mining function. N-grams are subsequences of length N drawn from a longer sequence. The purpose of the `ngrams` aggregate expression is to find the k most frequent n-grams from one or more sequences. This expression has the pattern of : ngrams(children: Array<Array<String>>(or Array<String>), n: Int, k: Int, accuracy: Int), all parameters are of `Expresion` type, I use the above way to indicate the type after evaluation. Among the parameters, children indicates the 'longer sequence' we collect n-grams from; n & k indicate the top k n-grams; accuracy is related to the memory used for frequency estimation, more memory will give more accurate frequency counts. ## How was this patch tested? Unit tests are in `NGramsQuerySuite` You can merge this pull request into a Git repository by running: $ git pull https://github.com/gczsjdy/spark UdafNGram Alternatively you can review and apply these changes as the patch at: https://github.com/apache/spark/pull/17359.patch To close this pull request, make a commit to your master/trunk branch with (at least) the following in the commit message: This closes #17359 ---- ---- --- If your project is set up for it, you can reply to this email and have your reply appear on GitHub as well. If your project does not have this feature enabled and wishes so, or if the feature is enabled but not working, please contact infrastructure at infrastruct...@apache.org or file a JIRA ticket with INFRA. --- --------------------------------------------------------------------- To unsubscribe, e-mail: reviews-unsubscr...@spark.apache.org For additional commands, e-mail: reviews-h...@spark.apache.org