# Hello everyone, I'm trying to write a function that returns an array with all path

**URL:** <https://discourse.julialang.org/t/hello-everyone-im-trying-to-write-a-function-that-returns-an-array-with-all-path/57296>\
**Category:** General Usage\
**Created:** [March 16, 2021, 12:30pm UTC](https://discourse.julialang.org/t/hello-everyone-im-trying-to-write-a-function-that-returns-an-array-with-all-path/57296 "2021-03-16T12:30:25Z")\
**Posts on this page:** 2\
**Page:** 1

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**Post date:** [March 16, 2021, 12:30pm UTC](https://discourse.julialang.org/t/hello-everyone-im-trying-to-write-a-function-that-returns-an-array-with-all-path/57296/1 "2021-03-16T12:30:25Z")

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Hello everyone,  
I’m trying to write a function that returns an array with all paths from root to leaves in a binary tree, where each path is an array of symbols.  
The tree struct is defined like this:

```julia
abstract type Node end

struct Branch_Node &lt;: Node
    left::Node
    right::Node
end

struct Leaf_Node &lt;: Node
end

```

So for this tree

```julia
tree = Branch_Node(Branch_Node(Branch_Node(Leaf_Node(), Leaf_Node()), Leaf_Node()),Branch_Node(Leaf_Node(), Leaf_Node()))

```

I want the function to return

```julia
[[:left, :left, :left], [:left, :left, :right], [:left, :right], [:right, :left], [:right, :right]]

```

I can write a function that returns a nested array like this:

```julia
function get_path_to_leaf(node::Leaf_Node)
    return
end
function get_path_to_leaf(node::Branch_Node)
    return [[:left, get_path_to_leaf(node.left)], [:right, get_path_to_leaf(node.right)]]
end

```

But I can’t figure out how to unfold the paths into flat arrays. I though something like this:

```julia
function get_path_to_leaf(node::Leaf_Node)
    return []
end

function get_path_to_leaf(node::Branch_Node)
    return [[append!([:left], i) for i in get_path_to_leaf(node.left)], [append!([:right], i) for i in get_path_to_leaf(node.right)]]
end

```

would do it, but I get the following error “ERROR: MethodError: Cannot `convert` an object of type Array{Symbol,1} to an object of type Symbol”  
and I’m having no luck debugging it. Sorry for the wall of text, can anyone help?

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**Author:** ![briochemc](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/briochemc/32/4209_2.png) [@briochemc](https://discourse.julialang.org/u/briochemc)\
**Post date:** [March 16, 2021, 1:32pm UTC](https://discourse.julialang.org/t/hello-everyone-im-trying-to-write-a-function-that-returns-an-array-with-all-path/57296/2 "2021-03-16T13:32:46Z")

</div>

I’m not entirely sure, but I don’t think this will work. Anytime you’d reach the leaf, you’d return an empty collection, which would “propagate” and give you an empty collection in the end. I think for something like this to work, you need to return a _non-empty_ thing with the leaf, even if it’s an 1-element vector containing an empty array of symbols:

```julia
julia> struct Branch_Node <: Node
           left::Node
           right::Node
       end

julia> struct Leaf_Node <: Node
       end

julia> function get_path_to_leaf(node::Leaf_Node)
           return [Symbol[]]
       end
get_path_to_leaf (generic function with 1 method)

julia> function get_path_to_leaf(node::Branch_Node)
           return [[[:left; x] for x in get_path_to_leaf(node.left)]; [[:right; x] for x in get_path_to_leaf(node.right)]]
       end
get_path_to_leaf (generic function with 2 methods)

julia> tree = Branch_Node(Branch_Node(Branch_Node(Leaf_Node(), Leaf_Node()), Leaf_Node()),Branch_Node(Leaf_Node(), Leaf_Node()))
Branch_Node(Branch_Node(Branch_Node(Leaf_Node(), Leaf_Node()), Leaf_Node()), Branch_Node(Leaf_Node(), Leaf_Node()))

julia> get_path_to_leaf(tree)
5-element Vector{Vector{Symbol}}:
 [:left, :left, :left]
 [:left, :left, :right]
 [:left, :right]
 [:right, :left]
 [:right, :right]

```