Question

All-

I am needing to change from a long format to a wide format in R, but I need the column values to be 1 or zero depending on if the particular variable is present for the subject.

The input data looks like:

Subject Product
    1   ProdA
    1   ProdB
    1   ProdC
    2   ProdB
    2   ProdC
    2   ProdD
    3   ProdA
    3   ProdB

and I want it to be

Subject ProdA   ProdB   ProdC   ProdD
    1   1   1   1   0
    2   0   1   1   1
    3   1   1   0   0

Is there any way in R to accomplish this?

EDIT:

One way I think is to first table the data:

tbl<-data.frame(table(data))

Then apply

final <- cast(tbl, Subject~Product, max)

I wonder if there is a more efficient way?

Answer 1

xtabs(data=dat)
       Product
Subject ProdA ProdB ProdC ProdD
      1     1     1     1     0
      2     0     1     1     1
      3     1     1     0     0

A slightly more readable version would make the fiormula explicit:

xtabs( ~Subject+Product, data=dat)

If you want to go with stats::reshape, then try this:

reshape(dat, idvar="Subject", timevar=2,   v.names="Product", direction="wide")
  Subject Product.ProdA Product.ProdB Product.ProdC Product.ProdD
1       1         ProdA         ProdB         ProdC          <NA>
4       2          <NA>         ProdB         ProdC         ProdD
7       3         ProdA         ProdB          <NA>          <NA>

(But it does not return numbers.)