[R] using apply to loop [SEC=UNCLASSIFIED]

[Crombie, Joe]

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 at brs.gov.au
 

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