R - return position of element in matrix?

问题

Given a matrix:

      [,1] [,2]
[1,]    0  0.0
[2,]   -1  0.8

What is the quickest way in R to iterate over the matrix and return the position of all non-zero entries as an index?

回答1:

Here is one approach

mat = matrix(rnorm(9), 3, 3)
which(mat !=0, arr.ind = T)

回答2:

m <- matrix(c(0, 1, 1, 0), nrow = 2)
which(m != 0)

or maybe

which(m != 0, TRUE)

来源：https://stackoverflow.com/questions/6522134/r-return-position-of-element-in-matrix