Hi there, I am wondering whether there is something similar to findfirst which does not return the index, but the matching object itself. This would be useful to work with Sets julia> findfirst(x->x==1,Set([1,2,3])) ERROR: MethodError: no method matching keys(::Set{Int64}) Closest candidates are…

function myfindfirst(f, s::Set) for i in s f(i) && return i end return nothing end is what you’re looking after ?

You could just test for membership: julia> 1 in Set([1,2,3]) true Or, if you need to match on more complex criteria: julia> any(mymatchfun, Set([1,2,3])) true (Hmm, but that doesn’t give you the object itself.) Maybe you can give an example use-case which does not trivially reduce to a simple m…

I guess the concept of finding the ‘first’ element that matches something in a set, doesn’t make sense, since sets are not ordered. It would be more akin to random sampling.

thank you all very much. I was hoping that there already exists something. But indeed. As the set is random, the name findfirst does not make much sense. Still the feature is useful and I very much like the simplicity of the myfindfirst function

You can also use first(Iterators.filter(==(1), s)). Note that this throws an error if no match is found. You can use first(..., 1) to get a 1-element vector if it is found and a 0-element vector if not.

Findfirst alternative for Set

General Usage

barucden May 23, 2023, 12:07pm 7

This thread is effectively asking the same question: Standard way to get first element of iterator satisfying predicate - #12 by simeonschaub

Topic		Replies	Views
Getting a specific item from a Set General Usage question , dictionary , set	7	428	October 15, 2022
First matching element in collection General Usage question	3	509	December 5, 2018
How to only read (first or last better) element of Set? General Usage	7	509	March 6, 2020
How do I access the elements of a set? New to Julia	3	185	September 24, 2025
Given S = Set{Vector{Int}}, how do I get a reference to the original object in S? General Usage dictionary	8	542	January 11, 2020

Findfirst alternative for Set

Related topics