# Error while using stack() with empty list Any\[ \]

**URL:** <https://discourse.julialang.org/t/error-while-using-stack-with-empty-list-any/117506>\
**Category:** New to Julia\
**Tags:** question\
**Created:** [July 26, 2024, 8:33am UTC](https://discourse.julialang.org/t/error-while-using-stack-with-empty-list-any/117506 "2024-07-26T08:33:59Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![Sahil\_Khan](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/sahil_khan/32/47573_2.png) [@Sahil\_Khan](https://discourse.julialang.org/u/Sahil_Khan)\
**Post date:** [July 26, 2024, 8:33am UTC](https://discourse.julialang.org/t/error-while-using-stack-with-empty-list-any/117506/1 "2024-07-26T08:33:59Z")

</div>

Hello everyone,

This is probably a very naive question but I don’t understand why i’m getting error in this case when i expect it to run perfectly. So In first example when I put main loop in test function I get error …while in second attempt when i keep it out it works perfectly.  
I think both cases should work.

MWE:

```julia
aaa = []

function fill_aaa(m)

    for i in 1:10
        push!(aaa, (i, "a", i+m))
    end
end

function test(aaa)
 
    for i in 1:5
        aaa = [] # I want it to be empty for each iteration  
       fill_aaa(i)
       stack(aaa, dims = 1)

    end

end

test(aaa)

```

Output:

```julia
ERROR: ArgumentError: `stack` on an empty collection is not allowed
Stacktrace:
 [1] _empty_stack(::Int64, ::Vararg{Any})
   @ Base ./abstractarray.jl:2903
 [2] _stack(dims::Int64, ::Base.HasShape{1}, iter::Vector{Any})
   @ Base ./abstractarray.jl:2810
 [3] _stack
   @ ./abstractarray.jl:2799 [inlined]
 [4] stack
   @ ./abstractarray.jl:2767 [inlined]
 [5] test(aaa::Vector{Any})
   @ Main ./Untitled-1:17
 [6] top-level scope
   @ Untitled-1:22

```

now if i remove function and just run loop—

```julia
for i in 1:5
    aaa = []
    fill_aaa(i)
    stack(aaa, dims = 1)

end

```

Output: This is exactly what I want.

```julia
julia> aaa
10-element Vector{Any}:
 (1, "a", 6)
 (2, "a", 7)
 (3, "a", 8)
 (4, "a", 9)
 (5, "a", 10)
 (6, "a", 11)
 (7, "a", 12)
 (8, "a", 13)
 (9, "a", 14)
 (10, "a", 15)

```

---

<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:** [July 26, 2024, 8:38am UTC](https://discourse.julialang.org/t/error-while-using-stack-with-empty-list-any/117506/2 "2024-07-26T08:38:29Z")

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Your function `fill_aaa(i)` captures the global variable `aaa`. It should take the empty collection that it is filling as an argument, i.e.

```julia
function fill_collection(x, m)
    for i in 1:10
        push!(x, (i, "a", i+m))
    end
end

```

---

<div class="post-metadata">

**Author:** ![Sahil\_Khan](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/sahil_khan/32/47573_2.png) [@Sahil\_Khan](https://discourse.julialang.org/u/Sahil_Khan)\
**Post date:** [July 26, 2024, 9:44am UTC](https://discourse.julialang.org/t/error-while-using-stack-with-empty-list-any/117506/3 "2024-07-26T09:44:46Z")

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it solves problem in MWE but still facing same issue in actual function :(. Maybe there is something else causing this issue.