I ran a benchmark. Code below.

##
Code

```
#!/bin/julia
using BenchmarkTools
using BenchmarkPlots
using StatsPlots
using Test
using Random: bitrand
BenchmarkTools.DEFAULT_PARAMETERS.seconds = 20
N = 10_000
preservingargmax = Dict{Symbol,Function}()
preservingargmax[:Inf] = (x, b) -> argmax(x .- Inf .* .!(b))
preservingargmax[:findall] = (x, b) -> findall(b)[argmax(x[b])]
preservingargmax[:findall_views] = (x, b) -> first(@view findall(b)[argmax(@view x[b])])
preservingargmax[:findnext] = (x, b) -> begin
c = argmax(x[b])
i0 = findfirst(identity, b)
for _ in 1:c-1
i0 = findnext(identity, b, i0 + 1)
end
return i0
end
preservingargmax[:findnext_views] = (x, b) -> begin
c = argmax(view(x, b))
i0 = findfirst(identity, b)
for _ in 1:c-1
i0 = findnext(identity, b, i0 + 1)
end
return i0
end
preservingargmax[:eachindex] = (x, b) -> eachindex(x)[b][argmax(x[b])]
preservingargmax[:eachindex_views] = (x, b) -> first(view(view(eachindex(x),b),argmax(view(x,b))))
preservingargmax[:sortperm] = (x, b) -> argmax(sortperm(x) .* b)
preservingargmax[:argmax] = (x, b) -> argmax(i -> b[i] ? x[i] : -Inf, eachindex(x))
preservingargmax[:enumerate] = (x, b) -> first(argmax(t -> t[2][1] ? t[2][2] : -Inf, enumerate(zip(b, x))))
preservingargmax[:zip] = (x, b) -> first(argmax(t -> t[2] ? t[3] : -Inf, zip(eachindex(x), b, x)))
preservingargmax[:loop] = (x, b) -> begin
maxx = -Inf
maxi = 0
for (xi, bi, i) in zip(x, b, eachindex(x))
(bi && xi > maxx) || continue
maxx = xi
maxi = i
end
return maxi
end
preservingargmax[:branchless] = (x, b) -> begin
maxx = -Inf
maxi = 0
for (xi, bi, i) in zip(x, b, eachindex(x))
maxi = (bi && xi > maxx)*i + !(bi && xi > maxx)*maxi
maxx = (bi && xi > maxx)*xi + !(bi && xi > maxx)*maxx
end
return maxi
end
preservingargmax[:to_index] = (x, b) -> (i=Base.to_index(b); Vector{Int}(i)[argmax(x[i])])
preservingargmax[:typemin] = (x, b) -> (y = copy(x); y[.!b] .= typemin(eltype(x)); argmax(y))
preservingargmax[:parentindices] = (x, b) -> (v = view(x, b); first(parentindices(v))[argmax(v)])
labels = [
:Inf,
:findall,
:findall_views,
:findnext,
:findnext_views,
:eachindex,
:eachindex_views,
:sortperm,
:argmax,
:enumerate,
:zip,
:loop,
:branchless,
:to_index,
:typemin,
:parentindices,
]
bg = BenchmarkGroup()
x_1 = [0, 2, 1, -3, 0]
b_1 = [true, false, true, true, false]
x_2 = collect(1:100)
b_2 = falses(100); b_2[[1, 3, 10, 100]] .= true
@testset "correctness, $k" for (k, f) in preservingargmax
@test f(x_1, b_1) == 3
@test f(x_2, b_2) == 100
bg[k] = @benchmarkable $f(x, b) setup = (x = randn($N); b = bitrand($N))
end
res = run(bg)
plot(
res,
labels,
;
yscale=:log10,
xrotation=30,
)
savefig("benchmark.png")
```