Is there an implementation of the MATLAB 3-output unique in Julia? In particular I’m looking for an efficient way to recreate the original input from the unique elements, like C(ic) in MATLAB. Previous discussions have focused on the indices of the unique elements (the ia output), but I haven’t fo…

How about this: function uniq(x) d = Dict{eltype(x), Int}() ia = Int[] ic = Vector{Int}(undef, length(x)) k = Ref(0) for (i, xx) in enumerate(x) ic[i] = get!(d, xx) do push!(ia, i) k[] += 1 end end u = Vector{eltype(x)}(undef, len…

If you only want unique values and indices ic, you can also use PooledArrays, eg using PooledArrays: PooledArray using DataAPI: refpool, refarray v = rand(["a", "b", "c"], 100) p = PooledArray(v) @assert v == refpool(p)[refarray(p)]

@mcabbott mentioned GroupSlices.jl, which has all the functions necessary to generate the vectors, but is several times slower than `unique. I managed to get an implementation that only works for vectors that replicates what Octave does, and it’s pretty close to the performance of unique while prov…

StructArrays also has some internal machinery that does the sorted approach. For the non-sorted I don’t know much other than PooledArrays, but it seems cheap enough to get ia from ic? Something like function find_ia(pool, ic) ia = fill(zero(eltype(ic)), length(pool)) for (i, idx) in enumer…

Sorry, meant to reply earlier, but you’re absolutely right. Thank you! I do need to remember not to @benchmark blocks of code; I almost tried to completely rewrite that to perform the same operation outside of an enumerate loop, but I just needed to do proper function wrapping. For some reason my i…

Yeah, here it’s a bit tricky because somehow the PooledArray constructor is type-unstable julia> using PooledArrays, Test julia> @inferred PooledArray(rand(1:3, 100)) ERROR: return type PooledVector{Int64, UInt32, Vector{UInt32}} does not match inferred return type PooledArray{Int64} so you do ne…

Luckily with PooledArray you can just specify your reftype in the constructor and it’s type-stable again, which is trivial for a lot of types, and can rely on UInt64 or even Int as a reasonable fallback.

MATLAB-like `unique` where you can recreate the original with indices

General Usage

t-bltg December 8, 2023, 8:05pm 9

I’ve posted a pure julia implementation in Unique (indices) method similar to MATLAB - #7 by t-bltg.

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MATLAB-like `unique` where you can recreate the original with indices

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