R help - Jun 2010 - Problem using apply

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]]

The mean by col and by row are the same:

colMeans(m) == rowMeans(m)

So:

m / rowMeans(m) # You don't need apply here
m / colMeans(m)

On Tue, Jun 1, 2010 at 2:26 PM, Joachim de Lezardiere <
joachim.lezard@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@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.
>


-- 
Henrique Dallazuanna
Curitiba-Paraná-Brasil
25° 25' 40" S 49° 16' 22" O

	[[alternative HTML version deleted]]

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@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@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.
>
	[[alternative HTML version deleted]]