[R] Recode factor into binary factor-level vars

[David Winsemius]

Sören;

You need to somehow add back to the information that is in "l" that  
fact that it was sampled from a set with 4 elements. Since you didn't  
sample from a factor the level information was lost. Otherwise, you  
coud create that list with unique(l) which in this case only returns 3  
elements:

set.l <- c("locA", "locB", "locC", "locD")

sapply(set.l,  function(x) l == x)
        locA  locB  locC  locD
  [1,] FALSE FALSE FALSE  TRUE
  [2,] FALSE FALSE FALSE  TRUE
  [3,] FALSE FALSE FALSE  TRUE
  [4,] FALSE FALSE FALSE  TRUE
  [5,] FALSE  TRUE FALSE FALSE
  [6,]  TRUE FALSE FALSE FALSE
  [7,]  TRUE FALSE FALSE FALSE
  [8,]  TRUE FALSE FALSE FALSE
  [9,] FALSE FALSE FALSE  TRUE
[10,]  TRUE FALSE FALSE FALSE

Its in the wrong orientation because "l" is actually a column vector,  
so t() fixes that and adding 0 to TRUE/FALSE returns 0/1:
t(sapply(set.l,  function(x) x == l))+0
      [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10]
locA    0    0    0    0    0    1    1    1    0     1
locB    0    0    0    0    1    0    0    0    0     0
locC    0    0    0    0    0    0    0    0    0     0
locD    1    1    1    1    0    0    0    0    1     0

m <- as.data.frame(t(sapply(set.l,  function(x) l == x))+0)
m

The one-liner would be:
m <- as.data.frame(t(sapply(c("locA", "locB", "locC", "locD"),   
function(x) l == x))+0)

You canalso you mapply but the result does not have the desired row  
names and the column names are the result of the sampling whcih seems  
to me potentially confusing:

 >  mapply(function(x) x==set.l, l)+0
      locD locD locD locD locB locA locA locA locD locA
[1,]    0    0    0    0    0    1    1    1    0    1
[2,]    0    0    0    0    1    0    0    0    0    0
[3,]    0    0    0    0    0    0    0    0    0    0
[4,]    1    1    1    1    0    0    0    0    1    0

I see that Dimitris has already given you a perfectly workable  
solution, but these seem to tackle the problem from a different angle.

-- 
David Winsemius, MD
Heritage Laboratories
West Hartford, CT

On Mar 7, 2009, at 8:39 AM, soeren.vogel at eawag.ch wrote:

> How to I "recode" a factor into a binary data frame according to the  
> factor levels:
>
> ### example:start
> set.seed(20)
> l <- sample(rep.int(c("locA", "locB", "locC", "locD"), 100), 10,  
> replace=T)
> # [1] "locD" "locD" "locD" "locD" "locB" "locA" "locA" "locA" "locD"  
> "locA"
> ### example:end
>
> What I want in the end is the following:
>
> m$locA: 0, 0, 0, 0, 0, 1, 1, 1, 0, 1
> m$locB: 0, 0, 0, 0, 1, 0, 0, 0, 0, 0
> m$locC: 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
> m$locD: 1, 1, 1, 1, 0, 0, 0, 0, 1, 0
>
> Instead of 0, NA's would also be fine.
>
> Thanks, Sören
>
> -- 
> Sören Vogel, PhD-Student, Eawag, Dept. SIAM
> http://www.eawag.ch, http://sozmod.eawag.ch
>
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