# First element of iteration satisfying a predicate
**URL:** https://discourse.julialang.org/t/first-element-of-iteration-satisfying-a-predicate/58617
**Category:** General Usage
**Tags:** question
**Created:** [April 5, 2021, 1:58pm UTC](https://discourse.julialang.org/t/first-element-of-iteration-satisfying-a-predicate/58617 "2021-04-05T13:58:13Z")
**Posts on this page:** 6
**Page:** 1
### Author:  [@Tamas\_Papp](https://discourse.julialang.org/u/Tamas_Papp)
#### Post date: [April 5, 2021, 1:58pm UTC](https://discourse.julialang.org/t/first-element-of-iteration-satisfying-a-predicate/58617/1 "2021-04-05T13:58:13Z")
I often find that I want to use something like `findfirst` on iterables that have no (or inefficient) random access, something like
```julia
function satisfies_first(predicate, itr)
for i in itr
predicate(i) && return Some(i)
end
nothing
end
julia> satisfies_first(iseven ∘ first, ((i, 2*i) for i in 1:10))
Some((2, 4))
```
It is pretty trivial to code this, but does this exist in a package somewhere? Or `Base`? I found [this discussion](https://discourse.julialang.org/t/standard-way-to-get-first-element-of-iterator-satisfying-predicate/25038/) about something similar, but I want to be careful about corner cases (element not found).
---
### Author:  [@Sukera](https://discourse.julialang.org/u/Sukera)
#### Post date: [April 5, 2021, 3:25pm UTC](https://discourse.julialang.org/t/first-element-of-iteration-satisfying-a-predicate/58617/2 "2021-04-05T15:25:38Z")
Possibly just chain `Iterators.filter(==(5), [1 2 3 4 5]) |> x -> isempty(x) ? nothing : first(x)`?
---
### Author:  [@Tamas\_Papp](https://discourse.julialang.org/u/Tamas_Papp)
#### Post date: [April 6, 2021, 11:28am UTC](https://discourse.julialang.org/t/first-element-of-iteration-satisfying-a-predicate/58617/3 "2021-04-06T11:28:58Z")
Sure, but that’s quite a mouthful for something so basic (and also note that it should give back `Something(first(x))`).
I will wait for more replies, then consider contributinga function not unlike the above to
[https://github.com/JuliaCollections/IterTools.jl](https://github.com/JuliaCollections/IterTools.jl)
---
### Author:  [@yakir12](https://discourse.julialang.org/u/yakir12)
#### Post date: [April 6, 2021, 11:47am UTC](https://discourse.julialang.org/t/first-element-of-iteration-satisfying-a-predicate/58617/4 "2021-04-06T11:47:40Z")
Maybe a bit nicer:
```julia
itr = ((i, 2i) for i in 1:10)
predicate = isodd ∘ first
using Base.Iterators
first(dropwhile(predicate, itr))
```
But this breaks if the collection is empty (there is no first to collect). Yea, nm. I’ll post this anyways…
---
### Author:  [@mschauer](https://discourse.julialang.org/u/mschauer)
#### Post date: [April 6, 2021, 12:02pm UTC](https://discourse.julialang.org/t/first-element-of-iteration-satisfying-a-predicate/58617/5 "2021-04-06T12:02:38Z")
I would perhaps define the generally useful
```julia
function someiterate(iter)
ϕ = iterate(iter)
ϕ === nothing && return nothing
return Some(first(ϕ))
end
```
instead and then it becomes
```julia
someiterate(dropwhile(predicate, itr))
```
you stay a bit longer in the “iterator-world”
---
### Author:  [@non-Jedi](https://discourse.julialang.org/u/non-Jedi)
#### Post date: [April 6, 2021, 12:08pm UTC](https://discourse.julialang.org/t/first-element-of-iteration-satisfying-a-predicate/58617/6 "2021-04-06T12:08:39Z")
People seemed open to the idea of adding that kind of functionality to Base, but I didn’t pursue it through until the PR was merged.
[https://github.com/JuliaLang/julia/pull/37119](https://github.com/JuliaLang/julia/pull/37119)