GroupSlices.jl

The function groupslices is related to unique, but instead of returning the unique elements, it returns a list of indices showing where an equivalent entry first appeared. Like this:

(v1.2) pkg> add GroupSlices

julia> using GroupSlices

julia> V = rand('α':'γ', 5)
5-element Array{Char,1}:
 'β'
 'β'
 'γ'
 'α'
 'β'

julia> groupslices(V)
5-element Array{Int64,1}:
 1
 1
 3
 4
 1

julia> unique(V)
3-element Array{Char,1}:
 'β'
 'γ'
 'α'

julia> M = rand(2:4, 2,13)
2×13 Array{Int64,2}:
 2  2  3  3  3  4  2  2  2  4  3  2  4
 4  4  4  4  4  4  3  4  3  2  3  4  2

julia> groupslices(M, dims=2) |> transpose
1×13 LinearAlgebra.Transpose{Int64,Array{Int64,1}}:
 1  1  3  3  3  6  7  1  7  10  11  1  10

julia> unique(M, dims=2)
2×6 Array{Int64,2}:
 2  3  4  2  4  3
 4  4  4  3  2  3

This package was written by AndyGreenwell in 2015, originally for Julia PRs #14142 and #15503.

My fork is now the registered version. It has minimal changes to make it work on Julia 1.0, and to accept keywords like dims=2 (although groupslices(M,2) will also still work).

See JuliaLang/julia#1845 for discussion of possible replacements.