Dear all,

I want to compare a huge vector with selected element from a matrix.

A is a matrix and B is a vector. I want to compare each element of B with
selected element from A. C and D are selection criteria. They are vectors
of same length as B. C specifies the row number of A, and D specifies the
column number. A is of dimension 10*100, and B,C,D are all vectors of
length 72000. Code with for loop:

   for ( j in 1:length(B) ){
      E[j] <- B[j] >= A[ C[j], D[j] ]
    }

This is too slow. I vectorize this by define a vector including elements
from A first:

    A1 <- array(0, length(B))
    A2 <- A[,D]
    for ( j in 1:length(B) ){
      A1[j] <- A2[ C[j], j ]
    }
    E <- B >= A1

This is still too slow. Is there a better way to this?


-- 
Kind regards,
Ran

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