Faster ways to calculate frequencies and cast from long to wide

ghz 1years ago ⋅ 8092 views

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 the counts as the values.

Example of what I've tried so far (tried a bunch of other things, including adding a dummy variable = 1 and then fun.aggregate = sum over that):

library(plyr)
ddply(data, .(id), dcast, id ~ week, value_var = "id", 
        fun.aggregate = length, fill = 0, .parallel = TRUE)

However, I must be doing something wrong because this function is not finishing. Is there a better way to do this?

Input:

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

Output:

  1  2  3
1 2  1  1
2 0  0  1

Answer

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
#r