# How to check if a condition is true for only one element in an array

**URL:** https://discourse.julialang.org/t/how-to-check-if-a-condition-is-true-for-only-one-element-in-an-array/52764
**Category:** New to Julia
**Created:** [January 3, 2021, 8:32am UTC](https://discourse.julialang.org/t/how-to-check-if-a-condition-is-true-for-only-one-element-in-an-array/52764 "2021-01-03T08:32:35Z")
**Posts on this page:** 5
**Page:** 1

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### Author: ![StevenSiew](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/stevensiew/32/218393_2.png) [@StevenSiew](https://discourse.julialang.org/u/StevenSiew)
#### Post date: [January 3, 2021, 8:32am UTC](https://discourse.julialang.org/t/how-to-check-if-a-condition-is-true-for-only-one-element-in-an-array/52764/1 "2021-01-03T08:32:35Z")

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I can do the following

```julia
julia> array = [1,3,4,7,9];

julia> All_numbers_are_positive = all(x->x>0,array)
true

julia> At_least_one_number_is_even = any(iseven,array)
true

```

But how do I do Only\_one\_number\_is\_even ?

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### Author: ![Skoffer](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/skoffer/32/378_2.png) [@Skoffer](https://discourse.julialang.org/u/Skoffer)
#### Post date: [January 3, 2021, 8:34am UTC](https://discourse.julialang.org/t/how-to-check-if-a-condition-is-true-for-only-one-element-in-an-array/52764/2 "2021-01-03T08:34:17Z")

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`count(iseven, array) == 1`

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<div class="post-metadata">

### Author: ![StevenSiew](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/stevensiew/32/218393_2.png) [@StevenSiew](https://discourse.julialang.org/u/StevenSiew)
#### Post date: [January 3, 2021, 8:47am UTC](https://discourse.julialang.org/t/how-to-check-if-a-condition-is-true-for-only-one-element-in-an-array/52764/3 "2021-01-03T08:47:29Z")

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How do I do

All\_numbers\_are\_not\_the\_same

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<div class="post-metadata">

### Author: ![jling](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/jling/32/212909_2.png) [@jling](https://discourse.julialang.org/u/jling)
#### Post date: [January 3, 2021, 8:57am UTC](https://discourse.julialang.org/t/how-to-check-if-a-condition-is-true-for-only-one-element-in-an-array/52764/4 "2021-01-03T08:57:57Z")

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is this homework related?

best performance:

```julia
any(!=(ary[1]), ary)

```

easy to write:

```julia
length(unique(ary)) > 1

```

* * *

also this can be improved to:

```julia
All_numbers_are_positive = all(>(0),array)

```

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<div class="post-metadata">

### Author: ![StevenSiew](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/stevensiew/32/218393_2.png) [@StevenSiew](https://discourse.julialang.org/u/StevenSiew)
#### Post date: [January 4, 2021, 1:11am UTC](https://discourse.julialang.org/t/how-to-check-if-a-condition-is-true-for-only-one-element-in-an-array/52764/5 "2021-01-04T01:11:28Z")

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No this is not a homework question

I need it for Monoalphabet Homophon Cryptography decoding program

I need it to look for symbols that appears only once.