Faster ways to calculate frequencies and cast from long to wide

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

You could just use the table command:

table(data$id,data$week)

    1 2 3
  1 2 1 1
  2 0 0 1

If "id" and "week" are the only columns in your data frame, you can simply use:

table(data)
#    week
# id  1 2 3
#   1 2 1 1
#   2 0 0 1