select vs select vs nsmallest in Julia

results.txt

julia> include("test_select.jl")
sz =     10, n =    5:
      select   :  mean: 0.00000065    median 0.00000058
      select!  :  mean: 0.00000043    median 0.00000040
      nsmallest:  mean: 0.00000112    median 0.00000104
sz =    100, n =    5:
      select   :  mean: 0.00000154    median 0.00000133
      select!  :  mean: 0.00000071    median 0.00000068
      nsmallest:  mean: 0.00000232    median 0.00000219
sz =    100, n =   50:
      select   :  mean: 0.00000270    median 0.00000258
      select!  :  mean: 0.00000161    median 0.00000140
      nsmallest:  mean: 0.00000962    median 0.00000902
sz =   1000, n =    5:
      select   :  mean: 0.00001061    median 0.00000778
      select!  :  mean: 0.00000442    median 0.00000408
      nsmallest:  mean: 0.00000562    median 0.00000519
sz =   1000, n =   50:
      select   :  mean: 0.00001140    median 0.00000928
      select!  :  mean: 0.00000534    median 0.00000524
      nsmallest:  mean: 0.00002582    median 0.00002498
sz =   1000, n =  500:
      select   :  mean: 0.00002625    median 0.00002485
      select!  :  mean: 0.00002040    median 0.00001934
      nsmallest:  mean: 0.00012084    median 0.00010682
sz =  10000, n =    5:
      select   :  mean: 0.00008258    median 0.00005986
      select!  :  mean: 0.00004765    median 0.00005017
      nsmallest:  mean: 0.00001785    median 0.00001747
sz =  10000, n =   50:
      select   :  mean: 0.00010093    median 0.00006327
      select!  :  mean: 0.00005606    median 0.00005195
      nsmallest:  mean: 0.00005383    median 0.00005039
sz =  10000, n =  500:
      select   :  mean: 0.00008543    median 0.00008394
      select!  :  mean: 0.00007592    median 0.00007553
      nsmallest:  mean: 0.00032306    median 0.00027703
sz =  10000, n = 5000:
      select   :  mean: 0.00033133    median 0.00028668
      select!  :  mean: 0.00029830    median 0.00028135
      nsmallest:  mean: 0.00137905    median 0.00122354
sz = 100000, n =    5:
      select   :  mean: 0.00079156    median 0.00083955
      select!  :  mean: 0.00055755    median 0.00060999
      nsmallest:  mean: 0.00013899    median 0.00013791
sz = 100000, n =   50:
      select   :  mean: 0.00085652    median 0.00075379
      select!  :  mean: 0.00054414    median 0.00059557
      nsmallest:  mean: 0.00018883    median 0.00018461
sz = 100000, n =  500:
      select   :  mean: 0.00091245    median 0.00084479
      select!  :  mean: 0.00057836    median 0.00051428
      nsmallest:  mean: 0.00057491    median 0.00054534
sz = 100000, n = 5000:
      select   :  mean: 0.00093798    median 0.00069805
      select!  :  mean: 0.00065583    median 0.00064509
      nsmallest:  mean: 0.00313060    median 0.00306621

select_nsmallest_comp.jl

using DataStructures

times_select = DefaultDict((Int,Int), Vector{Float64}, ()->Float64[])
times_select! = DefaultDict((Int,Int), Vector{Float64}, ()->Float64[])
times_nsmallest = DefaultDict((Int,Int), Vector{Float64}, ()->Float64[])

# warmup
select([1,2,3,4,5], 1:3)
nsmallest(3, [1,2,3,4,5])

for sz in [10, 100, 1000, 10000, 100000]
    for n in [5, 50, 500, 5000]
        n > sz && continue
        for iters = 1:div(1000000, sz)
            c = rand(-sz:sz, sz)
            c2 = copy(c)
            t_select = @elapsed select(c, 1:n)   # copies c
            t_select! = @elapsed select!(c, 1:n)  # modifies c
            t_nsmallest = @elapsed nsmallest(n, c2)
            push!(times_select[(sz, n)], t_select)
            push!(times_select![(sz, n)], t_select!)
            push!(times_nsmallest[(sz, n)], t_nsmallest)
        end
        times_select_sz_n = times_select[(sz, n)]
        times_select!_sz_n = times_select![(sz, n)]
        times_nsmallest_sz_n = times_nsmallest[(sz, n)]
        @printf("sz = %6d, n = %4d:\n", sz, n)
        @printf("      select   :  mean: %010.8f    median %010.8f\n", mean(times_select_sz_n),    median(times_select_sz_n))
        @printf("      select!  :  mean: %010.8f    median %010.8f\n", mean(times_select!_sz_n),   median(times_select!_sz_n))
        @printf("      nsmallest:  mean: %010.8f    median %010.8f\n", mean(times_nsmallest_sz_n), median(times_nsmallest_sz_n))
    end
end