# Whos element of vector y is in Set x

**URL:** <https://discourse.julialang.org/t/whos-element-of-vector-y-is-in-set-x/47065>\
**Category:** General Usage\
**Created:** [September 22, 2020, 12:59pm UTC](https://discourse.julialang.org/t/whos-element-of-vector-y-is-in-set-x/47065 "2020-09-22T12:59:01Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![programista](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/programista/32/5372_2.png) [@programista](https://discourse.julialang.org/u/programista)\
**Post date:** [September 22, 2020, 12:59pm UTC](https://discourse.julialang.org/t/whos-element-of-vector-y-is-in-set-x/47065/1 "2020-09-22T12:59:01Z")

</div>

I have a long vectros of strings. How to do this fasastest ?

```julia
julia> x=["a" "b"]
1×2 Array{String,2}:
 "a" "b"

julia> x=["a", "b"]
2-element Array{String,1}:
 "a"
 "b"

julia> y=["a","c","b","a","b"]
5-element Array{String,1}:
 "a"
 "c"
 "b"
 "a"
 "b"

julia> y in Set(x)
false

julia> y in. Set(x)
ERROR: syntax: invalid identifier name "."
Stacktrace:
 [1] top-level scope at none:1

julia> y .in Set(x)
ERROR: syntax: space before "." not allowed in "y ." at REPL[6]:1
Stacktrace:
 [1] top-level scope at none:1

julia> false
false'''

```

Paul

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<div class="post-metadata">

**Author:** ![nilshg](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/nilshg/32/2283_2.png) [@nilshg](https://discourse.julialang.org/u/nilshg)\
**Post date:** [September 22, 2020, 1:00pm UTC](https://discourse.julialang.org/t/whos-element-of-vector-y-is-in-set-x/47065/2 "2020-09-22T13:00:15Z")

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`in(Set(x)).(y)`

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<div class="post-metadata">

**Author:** ![DNF](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/dnf/32/10191_2.png) [@DNF](https://discourse.julialang.org/u/DNF)\
**Post date:** [September 22, 2020, 1:03pm UTC](https://discourse.julialang.org/t/whos-element-of-vector-y-is-in-set-x/47065/3 "2020-09-22T13:03:58Z")

</div>

Or

```julia
in.(y, (Set(x),))

```

or

```julia
y .∈ (Set(x),)

```

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<div class="post-metadata">

**Author:** ![tomerarnon](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/tomerarnon/32/3170_2.png) [@tomerarnon](https://discourse.julialang.org/u/tomerarnon)\
**Post date:** [September 22, 2020, 1:05pm UTC](https://discourse.julialang.org/t/whos-element-of-vector-y-is-in-set-x/47065/4 "2020-09-22T13:05:23Z")

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> [@DNF](#):
>
> `y .∈ (Set(x),)`

equivalently:

```julia
y .∈ Ref(Set(x))

```

My preferred in this case:

```julia
map(in(Set(x)), y) # or map(∈(Set(x)), y)

```