Some of the commonly used grouping function in `plyr` is listed following with simple example:

`apply`- It is used to apply a function to the rows or columns of a matrix, but not generally advisable for data frames as it will coerce to a matrix first.

# Two dimensional matrix mat <- matrix(seq(1,9), 3, 3)# apply min to rows apply(mat, 1, min)

`lapply`- It is used to apply a function to each element of a list, then get a list back and is the workhorse of other`ply`functions underneath the code.

x <- list(a = 1, b = 1:3, c = 10:50) lapply(x, FUN = length)

`sapply`- It is used to apply a function to each element of a list in turn, but get a vector back instead of a list.

x <- list(a = 1, b = 1:3, c = 10:50) ...