# Mean and empty collection

**URL:** https://discourse.julialang.org/t/mean-and-empty-collection/14496
**Category:** General Usage
**Tags:** question
**Created:** [September 3, 2018, 6:21pm UTC](https://discourse.julialang.org/t/mean-and-empty-collection/14496 "2018-09-03T18:21:29Z")
**Posts on this page:** 4
**Page:** 1

<div class="post-metadata">

### Author: ![gdkrmr](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/gdkrmr/32/2791_2.png) [@gdkrmr](https://discourse.julialang.org/u/gdkrmr)
#### Post date: [September 3, 2018, 6:21pm UTC](https://discourse.julialang.org/t/mean-and-empty-collection/14496/1 "2018-09-03T18:21:29Z")

</div>

`mean` behaves very inconsistently with empty collections, is this intentional?

```julia
julia> y = Union{Missing, Float64}[missing, missing, missing]

julia> mean(skipmissing(y))
ERROR: ArgumentError: mean of empty collection undefined: Base.SkipMissing{Array{Union{Missing, Float64},1}}(Union{Missing, Float64}[missing, missing, missing])

julia> mean(Float64[])
NaN

julia> mean(Int64[])
NaN

julia> mean([])
ERROR: MethodError: no method matching zero(::Type{Any})

```

---

<div class="post-metadata">

### Author: ![bkamins](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/bkamins/32/208538_2.png) [@bkamins](https://discourse.julialang.org/u/bkamins)
#### Post date: [September 3, 2018, 7:53pm UTC](https://discourse.julialang.org/t/mean-and-empty-collection/14496/2 "2018-09-03T19:53:27Z")

</div>

See [https://github.com/JuliaLang/julia/issues/28777](https://github.com/JuliaLang/julia/issues/28777)

---

<div class="post-metadata">

### Author: ![gdkrmr](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/gdkrmr/32/2791_2.png) [@gdkrmr](https://discourse.julialang.org/u/gdkrmr)
#### Post date: [September 4, 2018, 7:34am UTC](https://discourse.julialang.org/t/mean-and-empty-collection/14496/3 "2018-09-04T07:34:47Z")

</div>

thanks for the hint.

---

<div class="post-metadata">

### Author: ![bkamins](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/bkamins/32/208538_2.png) [@bkamins](https://discourse.julialang.org/u/bkamins)
#### Post date: [September 4, 2018, 7:41am UTC](https://discourse.julialang.org/t/mean-and-empty-collection/14496/4 "2018-09-04T07:41:31Z")

</div>

I am working on a PR to fix this.