SelectKBest for text analytics
Your Pipeline is now a model that expects similar input as before. You can use a CV scheme to choose your K inside your Pipeline, after it has evaluated the options and chosen the correct K it will use that to predict. For actual predictions, enter a list of tweets and it will classify them, no need to manually specify which features to use. If you want to know which features your Pipeline has chosen you can look in the properties of your 'p' object.