test.R

library(rbenchmark)
library(Matrix)

ncol <- 2e3
nrow <- 1e3
x <- matrix(rbinom(ncol * nrow, 1, 0.1), nrow = nrow, ncol = ncol)

benchmark(
  which(x != 0, arr.ind = T),                     # method 0
  which(Matrix(x, sparse = T) != 0, arr.ind = T), # method 1
  Matrix(x, sparse = T) |>                        # method 2
    (\(foo) {
      colN <- diff(foo@p)
      cbind(foo@i + 1, rep(seq_along(colN), colN))
    })(),
  replications = 100
)
# test         replications elapsed relative user.self sys.self user.child sys.child
# method 2              100    1.51    1.208      1.14     0.37         NA        NA
# method 1              100    1.99    1.592      1.59     0.39         NA        NA
# method 0              100    1.25    1.000      1.16     0.10         NA        NA