[R] Quickstart #2

[Jim Lemon]

Hi Phil,

This might get you started.

Read the file, converting it to an array:

data.array<-as.array(read.table("datafile",...))

then 'apply' the function 'stepvar':

data.var<-t(apply(data.array,1,stepvar))

Here's the function:

stepvar<-function(vec){
 veclen<-length(vec)
 while(veclen > 1) {
  vec[veclen]<-var(vec[1:veclen])
  veclen<-veclen-1
 }
 vec[1]<-NA
 return(vec)
}

'stepvar' replaces elements 2 to n of a vector with the variance of all
elements up to that element . (element 1 becomes NA).

You should then be able to plot successive rows of the original array
and the array of variances, perhaps even on the same plot, e.g.

plot(data.array[1,2:length(data.array[1,])])

points(data.var[1,2:length(data.var[1,])])

Hope this does what you want.

Jim

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