How to split a data frame by rows, and then process the blocks?

Question

I have a data frame with several columns, one of which is a factor called \"site\". How can I split the data frame into blocks of rows each with a unique value of \"site\",

Answer 1

There are two handy built in functions for dealing with these kind of situations. ?aggregate and ?by. In this case because you want a plot and aren't returning a scalar, use by()

data <- read.table("example.txt",header=TRUE)

by(data[, c('year', 'peak')], data$site, plot)

The output says NULL because that's what plot returns. You might want to set the graphics device to pdf to capture all the output.