On 27/02/2009 6:15 PM, Vemuri, Aparna wrote:
I have a large 3 dimensional array of size (243,246,768)
The first dimension is Rows, second is columns and the third is Time.
So for each row and column, I want to calculate the mean of time steps
1:8, 2:9, 3:10 and so on and assign the values to a new array. For this
I am using the following script.
for(i in 1:243)
{
for(j in 1:246)
{
for(k in 1:768)
{
newVar[i,j,k] <- mean( myVar[i,j,k:k+7])
}
}
}
This works, but needless to mention it take a very long time to loop
over all the rows, columns and time periods. I was wondering if there is
a simpler way to do this.
Yes, vectorize it. I think this would work:
newVar <- array(NA, c(243, 246, 768))
for (k in 1:768)
newVar[,,k] <- apply(myVar, 1:2, function(x) mean(x[k:(k+7)]))
but of course I haven't tried it.
Duncan Murdoch
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