Faster ways to calculate frequencies and cast from long to wide

Question

I am trying to obtain counts of each combination of levels of two variables, \"week\" and \"id\". I\'d like the result to have \"id\" as rows, and \"week\" as columns, and t

Answer 1

You don't need ddply for this. The dcast from reshape2 is sufficient:

dat <- data.frame(
    id = c(rep(1, 4), 2),
    week = c(1:3, 1, 3)
)

library(reshape2)
dcast(dat, id~week, fun.aggregate=length)

  id 1 2 3
1  1 2 1 1
2  2 0 0 1

---

Edit : For a base R solution (other than table - as posted by Joshua Uhlrich), try xtabs:

xtabs(~id+week, data=dat)

   week
id  1 2 3
  1 2 1 1
  2 0 0 1