sapply
Apply a function to every row of a matrix or a data frame
You simply use the apply() function: R> M <- matrix(1:6, nrow=3, byrow=TRUE) R> M [,1] [,2] [1,] 1 2 [2,] 3 4 [3,] 5 6 R> apply(M, 1, function(x) 2*x[1]+x[2]) [1] 4 10 16 R> This takes a matrix and applies a (silly) function to each row. You pass extra arguments to the function as … Read more
Grouping functions (tapply, by, aggregate) and the *apply family
R has many *apply functions which are ably described in the help files (e.g. ?apply). There are enough of them, though, that beginning useRs may have difficulty deciding which one is appropriate for their situation or even remembering them all. They may have a general sense that “I should be using an *apply function here”, … Read more