On Apr 13, 2009, at 10:54 AM, Brendan Morse wrote:
Hi everyone, I am having a bit of trouble correctly structuring an
equation in R.
Here is the equation
It's really a series of assignments.
Here is what I thought
for(i in 1:numItem)for(x in 1:numCat)
Ptheta[,i,x]<-(exp(-1.702*a[i]*(theta-b[i,x+1]))
I am guessing that what you really want is:
for(i in 1:numItem){
for(x in 1:numCat){
Ptheta[i,x]<-(exp(-1.702*a[i]*(theta-b[i,x+1]))
} } #obviously untested
That should populate the i, x entries of a matrix with your
calculations. The extra comma in your attempt was telling R that you
wanted a three dimensional array. The other possibility as a
construction would be to use expand.grid
My problem is that I am not sure how to get it to read the equation
as having two indexing points (i and x). Right now it is trying to
read it as a matrix, but each value (i and x) are only vectors.
Each value is an integer by the time it gets to the innards of the loop.
Does anyone have any suggestions on how to get R to recognize this?
As an example, numItem may = 20 and numCat may = 3 and I am trying
to evaluate this over all values of numCat for each value of numItem.
Thanks,
Brendan
--
David Winsemius, MD
Heritage Laboratories
West Hartford, CT
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