Question

I have a table that has a format along the lines of

user  data
1234  42
1234  51
1234  50
1235  61
1235  55

I want to create a histogram of the average “data” based on user. In other words, I would like to combine rows of the table with the same userID and come up with an average for them. How would I do this on a large dataset?

Answer 1

Just use tapply (assuming that your original data frame is named dat):

avgdata=tapply(dat$data,dat$user,FUN=mean)
hist(avgdata)