Transforms short text into a dictionary of TFIDF-weighted 3-gram
        character counts.

def short_text__str(self, column_name, output_column_prefix):
        """
        Transforms short text into a dictionary of TFIDF-weighted 3-gram
        character counts.
        """

        from ._ngram_counter import NGramCounter
        from ._tfidf import TFIDF

        return [NGramCounter(features=[column_name],
                             n = 3,
                             method = "character",
                             output_column_prefix = output_column_prefix),

                 TFIDF(features=[column_name],
                       min_document_frequency=0.01,
                       max_document_frequency=0.5,
                       output_column_prefix = output_column_prefix)]