R help - May 2008 - apply in apply

Dear list,

I need to apply a function on each column of each matrix contained in  
a list. Consider the following code,
> x <- 1:3
> my.data <- list(matrix(c(1,2,3,4,5,6),ncol=2),
> 		matrix(c(4,5,6,7,8,9),ncol=2))
>
> par(mfrow=c(2,2))
> results <- sapply(1:length(my.data),
> 			function(ii) apply(my.data[[ii]], 2, function(y) plot(x,y) )) #  
> plot is for demonstration purposes

It works, but I think this is quite dirty code. Is there a simpler  
way of achieving this? I was considering recasting the list into a  
matrix, apply the function to all its columns, and then reshape the  
result into an array of adequate dimensions, as in:
> results <- sapply(matrix(unlist(my.data),ncol= 2 * length 
> (my.data)), function(y) plot(x,y))
> #results <- matrix(results, ncol = length(my.data)) # when the  
> actual function is used instead of plot

but again it feels a bit twisted.

Best regards,

baptiste



_____________________________

Baptiste Augui?

Physics Department
University of Exeter
Stocker Road,
Exeter, Devon,
EX4 4QL, UK

Phone: +44 1392 264187

http://newton.ex.ac.uk/research/emag
http://projects.ex.ac.uk/atto

> I need to apply a function on each column of each matrix contained in 
> a list. Consider the following code,
> 
> > x <- 1:3
> > my.data <- list(matrix(c(1,2,3,4,5,6),ncol=2),
> >       matrix(c(4,5,6,7,8,9),ncol=2))
> >
> > par(mfrow=c(2,2))
> > results <- sapply(1:length(my.data),
> >          function(ii) apply(my.data[[ii]], 2, function(y) plot(x,y) ))
# 
> > plot is for demonstration purposes
> 
> 
> It works, but I think this is quite dirty code. Is there a simpler 
> way of achieving this?
The last line can be simplified
results <- sapply(my.data, function(x) apply(x,2,sum))

(It is perhaps a little clearer what is going on when you use sum rather 
than plot as the example function.)

Regards,
Richie.

Mathematical Sciences Unit
HSL


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