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a little probleme

4 messages · Olivier MARTIN, Guido Masarotto, Torsten Hothorn +1 more

Original
Olivier MARTIN
# 
Hi all,

i would like to find the best way to resolve the following problem.
Suppoose i have a vector x of length N with k different elements.
length(x)=N
u<-unique(x)
length(u)=k

I would like to get a matrix M with k rows and N columns such that:
in each line i (i=1,...,k), which(x%in%u[i]) is equal to 1 and 0 else.

Thanks for your help.
Olivier


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Olivier MARTIN               phone: (33) 04 76 61 53 55
Projet IS2                               06 08 67 93 42
INRIA Rhone-Alpes            fax  : (33) 04 76 61 54 77
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Montbonnot                  e-mail:olivier.martin at inrialpes.fr
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Guido Masarotto
#
On Wed, Jul 04, 2001 at 01:49:50PM +0200, Olivier Martin wrote:
You can try something along the lines of the following 
  small function (sort, colnames and rownames stuff are optional)

  try.me <- function(a)
  {
    n <- length(a)
    u <- sort(unique(a))
    m <- length(u)
    ans <- matrix(0,n,m)
    ans[rep(u,rep(n,m))==a] <- 1
    colnames(ans) <- u
    rownames(ans) <- a
    ans
  }

Example:
[1] 1 3 2 2 1 2 0 3 1 3
0 1 2 3
1 0 1 0 0
3 0 0 0 1
2 0 0 1 0
2 0 0 1 0
1 0 1 0 0
2 0 0 1 0
0 1 0 0 0
3 0 0 0 1
1 0 1 0 0
3 0 0 0 1
Chopin Debussy Mozart
Chopin       1       0      0
Mozart       0       0      1
Mozart       0       0      1
Debussy      0       1      0

or make use of the built-in model.matrix function which is essentially
equivalent to what you ask:
as.factor(a)Chopin as.factor(a)Debussy as.factor(a)Mozart
1                  1                   0                  0
2                  0                   0                  1
3                  0                   0                  1
4                  0                   1                  0
attr(,"assign")
[1] 1 1 1

guido



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Torsten Hothorn
# 
R> x <- c(1,2,3,3,4,4,5,6)
R> sapply(unique(x), fun <- function(a) x ==  a)
      [,1]  [,2]  [,3]  [,4]  [,5]  [,6]
[1,]  TRUE FALSE FALSE FALSE FALSE FALSE
[2,] FALSE  TRUE FALSE FALSE FALSE FALSE
[3,] FALSE FALSE  TRUE FALSE FALSE FALSE
[4,] FALSE FALSE  TRUE FALSE FALSE FALSE
[5,] FALSE FALSE FALSE  TRUE FALSE FALSE
[6,] FALSE FALSE FALSE  TRUE FALSE FALSE
[7,] FALSE FALSE FALSE FALSE  TRUE FALSE
[8,] FALSE FALSE FALSE FALSE FALSE  TRUE

which is as good as 0, 1 ;-)

Torsten
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Thomas Lumley
#
On Wed, 4 Jul 2001, Olivier Martin wrote:

            

      
      
      
    

        
Another solution

outer(unique(x),x,"==")+0

(the +0 just converts it to numeric rather than TRUE/FALSE)

	-thomas

Thomas Lumley			Asst. Professor, Biostatistics
tlumley at u.washington.edu	University of Washington, Seattle

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