Extracting Elements from a matrix

["Ilouga, Pierre" <Pierre.Ilouga@evotec.com>]

Dear Splus experts,

Does anyone has an idea how to extract some elements from a matrix in an EFFICIENT way? The following example clarifies  my question.

Given a  5x3 matrix  mat <- matrix(1:15, nrow=5, byrow=F)  and a length 5 -vector  of positions  pos <- c(2, 1, 3, 3, 1), the goal is to extract the vector c(6, 2, 13, 14, 5) which  corresponds to the column pos[j]  (j in 1:3) and row i  ( i in 1:5) without using for-loops and other memory consuming functions.

I’ve solve it via lists. However the slowness of the command executions doesn’t make it useful for  monte carlo simulation.

Thanks in advance.

PI

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Dr. Pierre Ilouga

Screening Operations/Discovery Informatics

EVOTEC AG

Schnackenburgallee 114

22525 Hamburg

Germany

pierre.ilouga@evotec.com

www.evotec.com

                   

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