I have a large data set with 3 columns: "survey", "time_interval", and "mass".
survey has an integer value from 1-3, and time_interval has an integer value from 1-8. Mass has decimal values. dataframe=JS_CU
How can I take mean of each time interval for each survey?
I tried to start by using group_by, but it I can't figure out how to input two criteria for the grouping. I get an error when I write this:
What's the best way to go about trying to get these means?