Thanks Joe,

It works well. How can I expand the output of z to include all other classes from 1 to nclass

Right now I the output is:
> z
          truth
classified  4  5  8 10
        1   1  1  1  0
        4   6 10  8  0
        10  1  0  1  1
> Is it possible to have something like:

    [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10] [,11] [,12]
 [1,]    0    0    0    1    1    0    0    1    0     0     0     0
 [2,]    0    0    0    0    0    0    0    0    0     0     0     0
 [3,]    0    0    0    0    0    0    0    0    0     0     0     0
 [4,]    0    0    0    6   10    0    0    8    0     0     0     0
 [5,]    0    0    0    0    0    0    0    0    0     0     0     0
 [6,]    0    0    0    0    0    0    0    0    0     0     0     0
 [7,]    0    0    0    0    0    0    0    0    0     0     0     0
 [8,]    0    0    0    0    0    0    0    0    0     0     0     0
 [9,]    0    0    0    0    0    0    0    0    0     0     0     0
[10,]    0    0    0    1    0    0    0    1    0     1     0     0
[11,]    0    0    0    0    0    0    0    0    0     0     0     0
[12,]    0    0    0    0    0    0    0    0    0     0     0     0

Thanks



"Crombie, Joe" <Joe.Crombie@brs.gov.au> a écrit : Hi Louis,

You could try this:

# find the index of the maximum value in each row of _data_, #
disregarding the last column classified <-
apply(data[,-(nclass+1)],1,which.max)

## or, if the maximum may be repeated:
classified <- apply(data[,-(nclass+1)], 1, FUN = function(x) which(x ==
max(x)))

# the variable _truth_ is just the last column of _data_ ?
truth <- data[,nclass + 1]

?table
z <- table(classified, truth)


HTH  Joe

 
Joe Crombie
 
Biosecurity and Information Sciences
Bureau of Rural Science
Canberra  Australia
 
e: joe.crombie@brs.gov.au
 

-----Original Message-----
From: r-help-bounces@r-project.org [mailto:r-help-bounces@r-project.org]
On Behalf Of Louis Martin
Sent: Friday, 21 December 2007 11:37 AM
To: R-help@r-project.org
Subject: [R] using apply to loop

Hi,

I am running the following loop, but it takes hours to run as n is big.
Is there any way "apply" can be used? Thanks.
### Start
    nclass <- dim(data)[[2]] - 1
    z <- matrix(0, ncol = nclass, nrow = nclass)
    n <- dim(data)[[1]]
    x <- c(1:nclass)
# loop starts
for(loop in 1:n) {
        r <- data[loop, 1:nclass]
        classified <- x[r == max(r)]
       
        truth <- data[loop, nclass + 1]
        z[classified, truth] <- z[classified, truth] + 1
    }
# loop ends


             
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