Extract the first TRUE per row in logical matrix efficiently in R [duplicate]

Answer 1

Here is my attempt. It isn't a one-liner, but it is lightning fast.

joe <-  function(x) {
    y <- which(x)
    nR <- nrow(x)
    myR <- y %% nR
    myR[myR==0] <- nR
    myNames <- colnames(x)[ceiling(y/nR)]
    myCols <- which(!(duplicated(myR)))
    myNames[myCols][order(myR[myCols])]
}

Here are the benchmarks using the data provided by @Cath:

microbenchmark(akrun(n), cath(n), joe(n))
Unit: microseconds
    expr       min        lq      mean    median        uq       max neval
akrun(n)  4248.760  5588.8640  6148.1816  5926.7130  6378.887 12502.437   100
 cath(n) 12641.189 13733.1415 14808.6524 14532.8115 15559.287 20628.037   100
  joe(n)   555.418   642.2405   758.5293   713.2585   800.697  4849.334   100

all.equal(akrun(n), cath(n), joe(n))
[1] TRUE