Julia: Sort Matrix by column 2 then 3
julia, matrix, sorting
Solution
There is a `sortslices` function that takes a `by` keyword that lets you do this:
julia> sortslices(A, dims=1, by=x->(x[2], x[3]))
100x4 Array{Float64,2}:
2.0 -3.0 -0.0 0.0
-1.0 -2.0 -1.0 -1.0
-0.0 -2.0 -0.0 0.0
0.0 -2.0 0.0 -1.0
1.0 -2.0 1.0 2.0
-0.0 -2.0 1.0 -1.0
-1.0 -1.0 -2.0 1.0
-1.0 -1.0 -2.0 -0.0
-1.0 -1.0 -1.0 1.0
-0.0 -1.0 -1.0 0.0
⋮
-0.0 1.0 1.0 -1.0
-0.0 1.0 2.0 1.0
0.0 1.0 2.0 0.0
-1.0 2.0 -2.0 1.0
0.0 2.0 -2.0 -2.0
1.0 2.0 -1.0 0.0
0.0 2.0 -1.0 -0.0
-1.0 2.0 0.0 -1.0
-0.0 2.0 2.0 0.0
1.0 3.0 2.0 1.0
The sorting API is pretty flexible – you can find documentation here.
Problem
I would like to sort my matrix `A` by column 2 then 3. ``` A = round.(randn(100,4)) ``` Maybe something like: ``` sort(A,(0,2:3)) 100x4 Array{Float64,2}: 0.0 -2.0 -2.0 -1.0 -1.0 -2.0 -1.0 1.0 1.0 -2.0 -1.0 2.0 -1.0 -2.0 0.0 0.0 -1.0 -2.0 0.0 -1.0 -0.0 -2.0 0.0 -1.0 1.0 -2.0 0.0 0.0 1.0 -2.0 1.0 -1.0 -0.0 -2.0 2.0 -1.0 -0.0 -1.0 -2.0 1.0 ⋮ -0.0 1.0 0.0 1.0 1.0 1.0 1.0 1.0 0.0 1.0 1.0 -1.0 -0.0 1.0 2.0 0.0 -0.0 2.0 -1.0 0.0 -2.0 2.0 -1.0 1.0 2.0 2.0 -0.0 -1.0 -1.0 2.0 -0.0 -1.0 1.0 2.0 0.0 2.0 -1.0 2.0 2.0 0.0 ```