Creating a node that writes certain topics to a csv file

edit

I want to create a node that writes a number of topics of my choice to a data file as they are streamed. I want to collect data so that they correspond to the same point in time (for this reason I am not using a rosbag and I plan to ignore the small time difference between them). After one set of values is written, repeat the same process. Could someone please point me to an example or some other resource that I can use.