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Using dcast to widen a data frame

I have the following data frame:

z <- data.frame(
                item=letters[rep(24:26,2)],
                freq=c(4,3,2,4,4,1),
                id=rep(1:2,each=3)
               )

item freq id
x    4    1
y    3    1
z    2    1
x    4    2
y    4    2
z    1    2

The data frame is unique on every id,item combination.

I would it to be like this:

id x y z
 1 4 3 2
 2 4 4 1

This looks like a fairly simple transform but I can't seem to get it to work.

Here is what I have tried (z is the name of the data frame):

dcast(z,id ~ item,sum)

and it returns this:

id x y z
1 1 1 1
2 2 2 2

What am I doing wrong?

Solution

  • I'm not sure why you're putting a "sum" function in there. Try this instead:

    > dcast(z, id ~ item, value.var="freq")
  id x y z
1  1 4 3 2
2  2 4 4 1