def remove_useless_phrases(docs_df):
    """ Remove phrases starting with a special character, and those which don't have a letter in them"""
    # Remove any rows which have phrase starting with special characters
    specialcharacters = ('|', '#', '*', '%', '@', '!', '~', '&', '>', '<', '\\', '/', '?', ';',
                         ':', ']', '[', '}', '{', '(', ')', '_', '-', '=', '+', '^')
    docs_df.drop(docs_df[docs_df.index.str.startswith(specialcharacters)].index, inplace=True)
    # Also, drop all phrases which do not contain a character (phrases composed of numbers and
    # special characters only. E.g. 25%, 13, 8&26 will all be dropped)
    pattern = r'[a-z]'
    # Use tilde for anything which doesn't match the pattern.
    docs_df.drop(docs_df[~docs_df.index.str.contains(pattern)].index, inplace=True)
    return docs_df