How to modify my timechart to get the results as i needed?

I have a search as follows in which I am trying to display 2 fields (My Search) | timechart span=1h count by field_username which displays the result as follows _time user_a user_b user_c user_d ---------------------------------- I don't want like this. All I am looking is as follows _time users_list_of_that_particullar_hour count_of_that_hour