# Reduce not type stable

**URL:** <https://discourse.julialang.org/t/reduce-not-type-stable/117056>\
**Category:** New to Julia\
**Created:** [July 15, 2024, 2:20pm UTC](https://discourse.julialang.org/t/reduce-not-type-stable/117056 "2024-07-15T14:20:09Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![ssdfg](https://avatars.discourse-cdn.com/v4/letter/s/a88e57/32.png) [@ssdfg](https://discourse.julialang.org/u/ssdfg)\
**Post date:** [July 15, 2024, 2:20pm UTC](https://discourse.julialang.org/t/reduce-not-type-stable/117056/1 "2024-07-15T14:20:09Z")

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```julia
julia> reduce(vcat, [1,2])
2-element Vector{Int64}:
 1
 2
julia> reduce(vcat, [1])
1

```

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<div class="post-metadata">

**Author:** ![DanielVandH](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/danielvandh/32/31134_2.png) [@DanielVandH](https://discourse.julialang.org/u/DanielVandH)\
**Post date:** [July 15, 2024, 2:23pm UTC](https://discourse.julialang.org/t/reduce-not-type-stable/117056/2 "2024-07-15T14:23:19Z")

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This thread [Inconsistency with `reduce(vcat, v)` when the vector has a single element](https://discourse.julialang.org/t/inconsistency-with-reduce-vcat-v-when-the-vector-has-a-single-element/75694) has some links to past discussions about this issue

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<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:** [July 15, 2024, 7:35pm UTC](https://discourse.julialang.org/t/reduce-not-type-stable/117056/3 "2024-07-15T19:35:25Z")

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Try passing an initial value:

```julia
julia> reduce(vcat, [1]; init=Int[])
1-element Vector{Int64}:
 1

```

Also `vcat` takes `k` collections so your current code treats `1` as a collection, which works because Julia numbers are iterable but it’s not that nice imo: I prefer to use real collections:

```julia
julia> reduce(vcat, [[1]]; init=Int[])
1-element Vector{Int64}:
 1

```