Column Indexes

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col(x)

col takes a matrix as argument and returns an integer matrix with the same dimensions. The ij-th element of col(x) is equal to j.

# extract the diagonal of a matrix dx <- x[row(x)==col(x)] # create an identity 5-by-5 matrix x <- matrix(0,nr=5,nc=5) x[row(x)==col(x)] <- 1