# Joining arrays of vectors of abritrary lengths

**URL:** <https://discourse.julialang.org/t/joining-arrays-of-vectors-of-abritrary-lengths/78880>\
**Category:** General Usage\
**Created:** [April 1, 2022, 4:25pm UTC](https://discourse.julialang.org/t/joining-arrays-of-vectors-of-abritrary-lengths/78880 "2022-04-01T16:25:09Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![juham58](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/juham58/32/33948_2.png) [@juham58](https://discourse.julialang.org/u/juham58)\
**Post date:** [April 1, 2022, 4:25pm UTC](https://discourse.julialang.org/t/joining-arrays-of-vectors-of-abritrary-lengths/78880/1 "2022-04-01T16:25:09Z")

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Hi,

I need to use arrays in which each element is a vector of arbitrary length. In itself, it works fine but when I try to append! an element to another array of vectors, it appends the vector to every elements of the target array. Obviously this is not what I want. Any ideas?

Creating a deepcopy of the element, appending to it and putting the deepycopy as the element works, but it is way too slow for what I am doing.

Here’s a working example of the problem:

```julia
stack = Array{Any}(undef, 2, 3, 3)
fill!(stack, Float64[])

stack[1, 1, 1] = [1.0, 2.0, 3.0]

merged_stack = Array{Any}(undef, 3, 3)
fill!(merged_stack, Float64[])

new_element = getindex(merged_stack, 1, 1)
merged_stack[1, 1] = append!(merged_stack[1, 1], stack[1, 1, 1])
println(merged_stack)

```

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<div class="post-metadata">

**Author:** ![oheil](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/oheil/32/220745_2.png) [@oheil](https://discourse.julialang.org/u/oheil)\
**Post date:** [April 1, 2022, 4:41pm UTC](https://discourse.julialang.org/t/joining-arrays-of-vectors-of-abritrary-lengths/78880/2 "2022-04-01T16:41:28Z")

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Your error is here:

```julia
julia> merged_stack = Array{Any}(undef, 3, 3)
3×3 Matrix{Any}:
 #undef #undef #undef
 #undef #undef #undef
 #undef #undef #undef

julia> fill!(merged_stack, Float64[])
3×3 Matrix{Any}:
 Float64[] Float64[] Float64[]
 Float64[] Float64[] Float64[]
 Float64[] Float64[] Float64[]

julia> append!(merged_stack[1,1],[1.0,2.0])
2-element Vector{Float64}:
 1.0
 2.0

julia> merged_stack
3×3 Matrix{Any}:
 [1.0, 2.0] [1.0, 2.0] [1.0, 2.0]
 [1.0, 2.0] [1.0, 2.0] [1.0, 2.0]
 [1.0, 2.0] [1.0, 2.0] [1.0, 2.0]

```

The `fill!` fills `merged_stack` with the same object. Alle the empty arrays `Float64[]` are a single object.  
There are several ways to achieve what you need, typically, I don’t have the most efficient way, but others will provide them.  
You can do with a loop for example:

```julia
julia> merged_stack = Array{Vector{Float64}}(undef, 3, 3)
3×3 Matrix{Vector{Float64}}:
 #undef #undef #undef
 #undef #undef #undef
 #undef #undef #undef

julia> for index in eachindex(merged_stack)
           merged_stack[index]=Float64[]
       end

julia> append!(merged_stack[1,1],[1.0,2.0])
2-element Vector{Float64}:
 1.0
 2.0

julia> merged_stack
3×3 Matrix{Any}:
 [1.0, 2.0] Float64[] Float64[]
 Float64[] Float64[] Float64[]
 Float64[] Float64[] Float64[]

```

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<div class="post-metadata">

**Author:** ![oheil](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/oheil/32/220745_2.png) [@oheil](https://discourse.julialang.org/u/oheil)\
**Post date:** [April 1, 2022, 4:45pm UTC](https://discourse.julialang.org/t/joining-arrays-of-vectors-of-abritrary-lengths/78880/3 "2022-04-01T16:45:24Z")

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I added the initialization, which was `Any` in your case. It’s best to use the Type you are using later.

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<div class="post-metadata">

**Author:** ![juham58](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/juham58/32/33948_2.png) [@juham58](https://discourse.julialang.org/u/juham58)\
**Post date:** [April 1, 2022, 4:54pm UTC](https://discourse.julialang.org/t/joining-arrays-of-vectors-of-abritrary-lengths/78880/4 "2022-04-01T16:54:01Z")

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Thank you this is exactly what I needed!