# Questions about missing

**URL:** https://discourse.julialang.org/t/questions-about-missing/87545
**Category:** General Usage
**Tags:** question
**Created:** [September 21, 2022, 6:23am UTC](https://discourse.julialang.org/t/questions-about-missing/87545 "2022-09-21T06:23:49Z")
**Posts on this page:** 3
**Page:** 1

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### Author: ![zhangchunyong](https://avatars.discourse-cdn.com/v4/letter/z/d9b06d/32.png) [@zhangchunyong](https://discourse.julialang.org/u/zhangchunyong)
#### Post date: [September 21, 2022, 6:23am UTC](https://discourse.julialang.org/t/questions-about-missing/87545/1 "2022-09-21T06:23:49Z")

</div>

```julia
julia> a=[true,false,true,true,missing]
5-element Vector{Union{Missing, Bool}}:
  true
 false
  true
  true
      missing
julia> mean(skipmissing(a))
0.75
julia> length(a)
5
julia> length(skipmissing(a))
ERROR: MethodError: no method matching length(::Base.SkipMissing{Vector{Union{Missing, Bool}}})

```

I want to calculate the length without missing in a,and only count the true and false ,then return 4.What should I do ? Thanks for helping me.

---

<div class="post-metadata">

### Author: ![jar1](https://avatars.discourse-cdn.com/v4/letter/j/c0e974/32.png) [@jar1](https://discourse.julialang.org/u/jar1)
#### Post date: [September 21, 2022, 6:44am UTC](https://discourse.julialang.org/t/questions-about-missing/87545/2 "2022-09-21T06:44:26Z")

</div>

You can use `collect`

```julia
julia> length(collect(skipmissing([1,2,missing,4])))
3

```

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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 21, 2022, 7:45am UTC](https://discourse.julialang.org/t/questions-about-missing/87545/3 "2022-09-21T07:45:10Z")

</div>

Or (probably more efficient)

```julia
count(!ismissing, a)

```