Is it possible to create a Set{MyType} that uses a custom hash and isequal functions s.t. it is essentially a set of equivalence classes w.r.t the equivalence relation defined by my hash and isequal? I want to do this without loosing my standard isequal that checks for full equality, and not only eq…

I’m not aware of a set type that does this. However, I think this would be a useful feature. For example, I might have a fast hash function for some custom type V{T} <: AbstractVector{T}, but it is not compatible with the default hash for vectors. This incompatibility does not matter for a Set with …

I can think of a solution: struct MyType coeff::Float64 indices::Vector{Int} end Base.hash(x::MyType, h::UInt) = hash(x.coeff, hash(x.indices, h)) Base.isequal(x::MyType, y::MyType) = (x.coeff == y.coeff) && (x.indices == y.indices) a = MyType(1., [2, 3]) b = MyType(2., [2, 3]) # False @…

In the end I settled to represent my Set{MyType} as a wrapped Dict{Vector{Int}, Float64}. Some (un)wrapping was required to turn insertion of a MyType into insertion of a Vector{Int} => Float64 into that dict and make iteration yield MyType instead of Pair{Vector{Int}, Float64}, but I hope that the…

Great minds think alike :smiley: Your solutoin works as well and is similar to my solution above in that additional (un)wrapping would be needed to be able to directly insert MyTypes and have iteration yield MyTypes instead of MyWrapper.

[image] jlbosse: Great minds think alike :smiley: :grinning_face: Using Dict is way more convenient. You can avoid wrapping/unwrapping too: function store_mytype!(dict::AbstractDict, x::MyType) get!(dict, x.indices) do x end end dict = Dict{Vector{Int}, MyType}() store_myty…

[image] jlbosse: Is it possible to create a Set{MyType} that uses a custom hash and isequal functions See: [image] Dictionary with custom hash function General Usage Just wrap your keys in a new type: struct MyKey val::UInt end Base.hash(a::MyKey, h::UInt) = x…

Dictionary with custom hash function Just wrap your keys in a new type Sure, but then you have to unwrap the elements again when you want to use methods defined for the original type – if that it possible at all. Maybe the elements are used inside a function defined in some third-party packag…

Create a set with custom hash and isequal

General Usage

stevengj April 9, 2025, 3:07pm 7

See:

Topic		Replies	Views
Set with type with custom equality General Usage	3	176	June 8, 2024
Set inconsistencies with structs General Usage question	4	520	May 6, 2021
Create a user-type set General Usage type , set , hash	2	621	January 29, 2022
How to define `:(==)` on user-defined types for `Set` operations General Usage sets	2	137	March 3, 2025
Struct equality seems weird inside Sets General Usage set , struct , isequal	6	1051	December 5, 2020

Create a set with custom hash and isequal

Related topics