From: Peter Langfelder <peter.langfelder_at_gmail.com>

Date: Tue, 01 Jun 2010 10:45:14 -0700

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https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. Received on Tue 01 Jun 2010 - 17:48:43 GMT

Date: Tue, 01 Jun 2010 10:45:14 -0700

Well, your example matrix is symmetric, so row and column operations naturally return the same values.

You may want to note though that if you apply your function to a matrix along rows, the results will be stored in the __columns__ of the resulting matrix. Thus, if you want to simply divide the rows of a matrix by their mean, you need to transpose the result.

Example:

m = matrix(c(0,1,2,5), 2,2)

m

apply( m, 1, divideByMean)

t(apply( m, 1, divideByMean)) # This is what you probably want.

**HTH,
**
Peter

On Tue, Jun 1, 2010 at 10:26 AM, Joachim de Lezardiere < joachim.lezard_at_gmail.com> wrote:

> Hello ,

*>
**>
**>
**> I can not get apply function to do what I want when doing stuff on rows.
**> Let's say I want to divide the rows of matrix by their mean, the below show
**> you get the same result weather you use 1 or 2, i.e. same result for
**> columns
**> than for means..:(
**>
**>
**>
**> Thanks a lot for the help,
**>
**>
**>
**>
**>
**>
**>
**> m = matrix( c(1,4,7,4,5,8,7,8,9), nrow = 3 )
**>
**>
**>
**> divideByMean = function( v ){
**>
**> return( v/mean(v))
**>
**> }
**>
**>
**>
**> rowMean = c( mean( m[1,]),mean( m[2,]),mean( m[3,]) )
**>
**> rowMean
**>
**>
**>
**> colMean = c( mean( m[,1]),mean( m[,2]),mean( m[,3]) )
**>
**> colMean
**>
**>
**>
**> m
**>
**> print("ByRow")
**>
**> apply( m, 1, divideByMean)
**>
**>
**>
**> print("ByCol")
**>
**> apply( m, 2, divideByMean)
**>
**>
**>
**>
**>
**>
**>
**>
**> [[alternative HTML version deleted]]
**>
**> ______________________________________________
**> R-help_at_r-project.org mailing list
**> https://stat.ethz.ch/mailman/listinfo/r-help
**> PLEASE do read the posting guide
**> http://www.R-project.org/posting-guide.html
**> and provide commented, minimal, self-contained, reproducible code.
**>
*

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https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. Received on Tue 01 Jun 2010 - 17:48:43 GMT

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