Range (statistics)

Specific Domains Statistics
12

Fixing this does not entail so much overhead:

function range4(x)
    isempty(x) && error("Does not support empty vectors")
    min = typemax(eltype(x))
    max = typemin(eltype(x))
    hasnan = false
    for xi in x
        hasnan |= isnan(xi)
        min = ifelse(min > xi, xi, min)
        max = ifelse(max < xi, xi, max)
    end
    hasnan && error("Does not support NaNs in vectors")
    return max - min
end

julia> x = 10 * rand(100);

julia> y = 10 * rand(1000000);

julia> @btime range4($x);
  107.822 ns (0 allocations: 0 bytes)

julia> @btime extrema($x);
  318.175 ns (0 allocations: 0 bytes)

julia> @btime range4($y);
  1.397 ms (0 allocations: 0 bytes)

julia> @btime extrema($y);
  3.285 ms (0 allocations: 0 bytes)

There is a ~3X gap here (persisting into large vectors), and this trivial (and popular) operation could probably be optimized further (SIMD, threads etc.)

2 Likes