[R] t.tests on a data.frame using an apply-type function

I have a data.frame with ~250 observations (rows) in each of ~50 categories (columns). I would like to perform t.tests on subsets of observations within each column, with the subsets according to index vectors contained in other columns of the data.frame. My data.frame looks something

Re: [R] t.tests on a data.frame using an apply-type function

Try this: lapply(split(x, x$site), function(.x){ .xl - split(.x[-(1:2)], .x$status) mapply(t.test, .xl[[1]], .xl[[2]], SIMPLIFY = FALSE) }) On Sat, Aug 21, 2010 at 11:15 AM, Alison Macalady a...@kmhome.org wrote: I have a data.frame with ~250 observations (rows) in each of ~50 categories

Re: [R] t.tests on a data.frame using an apply-type function

Hi: Henrique's solution is elegant, but if you want to summarize certain features of the test (e.g., the value of the test statistic and its p-value), then here's a different approach using packages reshape and plyr. # Since your data in group C had a sample size of 2, I redid the data frame