# Find n smallest values in an n dims array

**URL:** <https://discourse.julialang.org/t/find-n-smallest-values-in-an-n-dims-array/81092>\
**Category:** New to Julia\
**Tags:** question, sort, sortperm, arrays, cartesianindices\
**Created:** [May 15, 2022, 12:07pm UTC](https://discourse.julialang.org/t/find-n-smallest-values-in-an-n-dims-array/81092 "2022-05-15T12:07:22Z")\
**Posts on this page:** 1\
**Showing post:** 13

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**Author:** ![JM\_Beckers](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/jm_beckers/32/22482_2.png) [@JM\_Beckers](https://discourse.julialang.org/u/JM_Beckers)\
**Post date:** [May 15, 2022, 8:03pm UTC](https://discourse.julialang.org/t/find-n-smallest-values-in-an-n-dims-array/81092/13 "2022-05-15T20:03:47Z")

</div>

I think this version is not optimal if n is very small compared to the size of the array since you make a full sort and just retain a few smallest values. At the limit, imagine to get the lowest value of an array you make a sort first. That does not sound right. A dirty write-up like the following

```julia
using BenchmarkTools
A=rand(100,100,10,40,10);
function arg_n_smallest_values(A::AbstractArray{T,N}, n::Integer) where {T,N}
           perm = sortperm(vec(A))
           ci = CartesianIndices(A)
           return ci[perm[1:n]]
       end
function argsmallest(A::AbstractArray{T,N}, n::Integer) where {T,N}
           # should someone ask more elements than array size, just sort array
       
           if n>= length(vec(A))
             ind=collect(1:length(vec(A)))
             ind=sortperm(A[ind])
             return CartesianIndices(A)[ind]
           end
           # otherwise 
           ind=collect(1:n)
           mymax=maximum(A[ind])
           for j=n+1:length(vec(A))
           if A[j]<mymax
            getout=findmax(A[ind])[2]
            ind[getout]=j
            mymax=maximum(A[ind])
           end
           end
           ind=ind[sortperm(A[ind])]
           
           return CartesianIndices(A)[ind]
       end

@btime arg_n_smallest_values(A,5) # 16.61 s
@btime argsmallest(A,5) # 42 ms

```

already greatly improves the timing, but I’m sure there are even better ways ?

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