# Comparing with nothing

**URL:** <https://discourse.julialang.org/t/comparing-with-nothing/37888>\
**Category:** General Usage\
**Created:** [April 20, 2020, 10:00am UTC](https://discourse.julialang.org/t/comparing-with-nothing/37888 "2020-04-20T10:00:17Z")\
**Posts on this page:** 10\
**Page:** 1

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**Author:** ![hmemy](https://avatars.discourse-cdn.com/v4/letter/h/50afbb/32.png) [@hmemy](https://discourse.julialang.org/u/hmemy)\
**Post date:** [April 20, 2020, 10:00am UTC](https://discourse.julialang.org/t/comparing-with-nothing/37888/1 "2020-04-20T10:00:17Z")

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How to compare with the value **nothing**? I came up with this small piece of lines but it is not working.

```julia
A = [1,2,3]
if indexin(USER_INPUT,A) !== nothing
       do_someething()
       end

```

Thank you

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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:** [April 20, 2020, 10:04am UTC](https://discourse.julialang.org/t/comparing-with-nothing/37888/2 "2020-04-20T10:04:33Z")

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```julia
julia> isnothing(nothing)
true

```

---

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**Author:** ![kristoffer.carlsson](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/kristoffer.carlsson/32/22_2.png) [@kristoffer.carlsson](https://discourse.julialang.org/u/kristoffer.carlsson)\
**Post date:** [April 20, 2020, 10:06am UTC](https://discourse.julialang.org/t/comparing-with-nothing/37888/3 "2020-04-20T10:06:34Z")

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`indexin` returns an `Array` so `!== nothing` will always be `true`. What do you want to do?

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<div class="post-metadata">

**Author:** ![hmemy](https://avatars.discourse-cdn.com/v4/letter/h/50afbb/32.png) [@hmemy](https://discourse.julialang.org/u/hmemy)\
**Post date:** [April 20, 2020, 10:11am UTC](https://discourse.julialang.org/t/comparing-with-nothing/37888/4 "2020-04-20T10:11:25Z")

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The USE\_INPUT is an integer.

indexin(2,A) results in 2  
but indexin(4,A) results in nothing.

So, I would like to compare with the result.

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<div class="post-metadata">

**Author:** ![pfitzseb](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/pfitzseb/32/45566_2.png) [@pfitzseb](https://discourse.julialang.org/u/pfitzseb)\
**Post date:** [April 20, 2020, 10:14am UTC](https://discourse.julialang.org/t/comparing-with-nothing/37888/5 "2020-04-20T10:14:03Z")

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As Kristoffer said, those are (zero dimensional) arrays. You could e.g. try

```julia
julia> any(isnothing, indexin(1, [1,2,3]))
false

julia> any(isnothing, indexin(9, [1,2,3]))
true

```

---

<div class="post-metadata">

**Author:** ![kristoffer.carlsson](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/kristoffer.carlsson/32/22_2.png) [@kristoffer.carlsson](https://discourse.julialang.org/u/kristoffer.carlsson)\
**Post date:** [April 20, 2020, 10:17am UTC](https://discourse.julialang.org/t/comparing-with-nothing/37888/6 "2020-04-20T10:17:15Z")

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Why not use `if USER_INPUT in A` instead?

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<div class="post-metadata">

**Author:** ![hmemy](https://avatars.discourse-cdn.com/v4/letter/h/50afbb/32.png) [@hmemy](https://discourse.julialang.org/u/hmemy)\
**Post date:** [April 20, 2020, 10:17am UTC](https://discourse.julialang.org/t/comparing-with-nothing/37888/7 "2020-04-20T10:17:26Z")

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```julia
if any(isnothing, indexin(9, [1,2,3])) === false
       println("wahoo")
       end

```

It works well,  
Thank you

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<div class="post-metadata">

**Author:** ![hmemy](https://avatars.discourse-cdn.com/v4/letter/h/50afbb/32.png) [@hmemy](https://discourse.julialang.org/u/hmemy)\
**Post date:** [April 20, 2020, 10:18am UTC](https://discourse.julialang.org/t/comparing-with-nothing/37888/8 "2020-04-20T10:18:35Z")

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I am new Julia user. can you provide an example?

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<div class="post-metadata">

**Author:** ![kristoffer.carlsson](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/kristoffer.carlsson/32/22_2.png) [@kristoffer.carlsson](https://discourse.julialang.org/u/kristoffer.carlsson)\
**Post date:** [April 20, 2020, 10:19am UTC](https://discourse.julialang.org/t/comparing-with-nothing/37888/9 "2020-04-20T10:19:26Z")

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```julia
if 9 in [1,2,3]
    println("wahoo")
end

if 2 in [1,2,3]
    println("wohoo")
end

```

---

<div class="post-metadata">

**Author:** ![hmemy](https://avatars.discourse-cdn.com/v4/letter/h/50afbb/32.png) [@hmemy](https://discourse.julialang.org/u/hmemy)\
**Post date:** [April 20, 2020, 10:20am UTC](https://discourse.julialang.org/t/comparing-with-nothing/37888/10 "2020-04-20T10:20:55Z")

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This also works. Thank you