Ulog timestamp matching


I am examining ulog file from a flight test and trying to perform a simple system identification. I am using python and read to ulog file in dataframes for different topics such as t_actuator_controls_3_0, t_flight_analysis_0, etc. I noticed that the data doesnt have matching timestamps and when I try to merge them on time column it normally produces lots of rows with NaN values. I was wondering if it is possible to perform a matching the data with respect to same timestamp values.