Reduce not type stable

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

This thread Inconsistency with `reduce(vcat, v)` when the vector has a single element has some links to past discussions about this issue

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3

Try passing an initial value:

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