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

I seem to recall that plain old split() has a method for data.frames, so that split(data,data$site) would produce a list of blocks. You could then operate on this list using sapply/lapply/for.

split() is also nice because of unsplit(), which will create a vector the same length as the original data and in the correct order.