How to use cast or another function to create a binary table in R

Question

I am trying to create a list of factors that have a binary response and have been using cast.

DF2 <- cast(data.frame(DM), id ~ region)
names(DF2)[-1] <         


        

Answer 1

No specialized functions are needed:

x <- data.frame(id=1:4, region=factor(c(3,2,1,2)))
x
   id region
1  1      3
2  2      2
3  3      1
4  4      2

x.bin <- data.frame(x$id, sapply(levels(x$region), `==`, x$region))
names(x.bin) <- c("id", paste("region", levels(x$region),sep=''))
x.bin

  id region1 region2 region3
1  1   FALSE   FALSE    TRUE
2  2   FALSE    TRUE   FALSE
3  3    TRUE   FALSE   FALSE
4  4   FALSE    TRUE   FALSE

Or for integer results:

x.bin2 <- data.frame(x$id,  
    apply(sapply(levels(x$region), `==`, x$region),2,as.integer)
) 
names(x.bin2) <- c("id", paste("region", levels(x$region),sep=''))
x.bin2


  id region1 region2 region3
1  1       0       0       1
2  2       0       1       0
3  3       1       0       0
4  4       0       1       0

Answer 2

Original data:

x <- data.frame(id=c(1,1,2,3,3), region=factor(c(2,3,2,1,1)))

> x
  id region
1  1      2
2  1      3
3  2      2
4  3      1
5  3      1

Group up the data:

aggregate(model.matrix(~ region - 1, data=x), x["id"], max)

Result:

  id region1 region2 region3
1  1       0       1       1
2  2       0       1       0
3  3       1       0       0

Answer 3

I kind of prefer dcast from reshape2:

library(reshape2)
dat <- read.table(text = "id region
 1   2
 1   3
 2   2
 3   1
 3   1",header = TRUE,sep = "")

dcast(dat,id~region,fun.aggregate = function(x){as.integer(length(x) > 0)})

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

There may be a smoother way to do that, but I'll be honest I don't cast stuff all that often.

Answer 4

Here's sort of a "tricky" way to do it in one line using table (the brackets are important). Assuming your data.frame is named df:

(table(df) > 0)+0
#    region
# id  1 2 3
#   1 0 1 1
#   2 0 1 0
#   3 1 0 0

table(df) > 0 gives us TRUE and FALSE; adding +0 converts the TRUE and FALSE to numbers.