[R] dividing a matrix by positive sum or negative sum depending on the sign

[Dimitris Rizopoulos]

one approach is the following:

mat <- rbind(c(-1, -1, 2, NA), c(3, 3, -2, -1), c(1, 1, NA, -2))

mat / ave(abs(mat), row(mat), sign(mat), FUN = sum)


I hope it helps.

Best,
Dimitris


Hao Cen wrote:
> Hi,
> 
> I have a matrix with positive numbers, negative numbers, and NAs. An
> example of the matrix is as follows
> 
> -1 -1 2 NA
> 3 3 -2 -1
> 1 1 NA -2
> 
> I need to compute a scaled version of this matrix. The scaling method is
> dividing each positive numbers in each row by the sum of positive numbers
> in that row and  dividing each negative numbers in each row by the sum of
> absolute value of negative numbers in that row.
> 
> So the resulting matrix would be
> 
> -1/2 -1/2 2/2 NA
> 3/6 3/6 -2/3 -1/3
> 1/2 1/2 NA -2/2
> 
> Is there an efficient way to do that in R? One way I am using is
> 
> 1. rowSums for positive numbers in the matrix
> 2. rowSums for negative numbers in the matrix
> 3. sweep(mat, 1, posSumVec, posDivFun)
> 4. sweep(mat, 1, negSumVec, negDivFun)
> 
> posDivFun = function(x,y) {
>         xPosId = x>0 & !is.na(x)
>         x[xPosId] = x[xPosId]/y[xPosId]
>         return(x)
> }
> 
> negDivFun = function(x,y) {
>         xNegId = x<0 & !is.na(x)
>         x[xNegId] = -x[xNegId]/y[xNegId]
>         return(x)
> }
> 
> It is not fast enough though. This scaling is to be applied to large data
> sets repetitively. I would like to make it as fast as possible. Any
> thoughts on improving it would be appreciated.
> 
> Thanks
> 
> Jeff
> 
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-- 
Dimitris Rizopoulos
Assistant Professor
Department of Biostatistics
Erasmus University Medical Center

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