Thanks, Peter and Henrik.

Vasu.


On 11/30/05, Henrik Bengtsson <hb@maths.lth.se> wrote:
>
> Vasundhara Akkineni wrote:
> > I have another issue.i have a function which calculates the log2(col i
> > /col2) value, where i stands for columns 3,4,...etc.
> >
> > data<-read.table("table.txt", header=TRUE)
> >
> > iratio<-function(x){
> > for(n in 3:ncol(data)){
> > z<-log2(data[x,n]/data[x,2])
> > }
> > }
> >
> > Where x- the row number of the data frame(data).
> >
> > i want to store the ratios for each row in a object z,  which can be
> > accessed outside the function. How can i do this?
>
> Just return the result at the end of the function.  Since you want to
> return log-ratios for many pairs, I would suggest to stick them in a new
> data frame, or since they results are all of the same data type, a
> matrix instead. Example:
>
> iratio <- function(rows) {
>   # Create (pre-allocate) empty matrix poulated with NAs
>   z <- matrix(NA, nrow=length(x), ncol=ncol(data)-3+1);
>
>   for(col in 3:ncol(data)) {
>     z[,col-3+1] <- log2(data[rows,col] / data[rows,2])
>   }
>
>   z;  # or equivalent 'return(z)'; not often seen in R code.
> }
>
> You should try to look into introductions to R (sorry I don't know any
> off hand, but just search google); this is all things you need to learn.
> Also, you learn a lot from reading other people's code snippets.
>
> When you understand R better, you'll also realize that the above can be
> done in one line of code like this:
>
>   z <- log2(data[rows,3:ncol(data)] / data[rows,2]);
>
> Cheers
>
> Henrik
>
> PS. I haven't actually tested the above code in R; there might be typos.
> DS.
>
> > Thanks,
> > Vasu.
> >
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> >
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> >
>
>

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