Append! on arrays of arryas

General Usage
1

I want to create an array of empty arrays so I can append and have different sized arrays like this:
append_on_brackets

But, if I use fill to create the array of empty arrays and then I append it the result is this:

append_on_fill
append_on_fill296×594 19.8 KB

Why is it any different when initializing the array of arrys with fill? Does it have to do with how it saves to memory?

I found out how to initialize my array of a given number of arryays like this:

N=10
a=[]
for n in 1:N
    push!(a,[])
end

Doing it like this allows me to append it the way I want.

2

In the fill example, you are creating a single array pointing to some memory on the heap. This is passed into the fill function and sets every element pointing at that same array.

To get what you want, you have to create a new array for each element, e.g. with a list comphrension:

arr=[[] for _ in 1:10]
3

The Julia documentation for the fill() covers this explicitly.
?fill in the Julia REPL will show you this. It is also available
in the online Julia documentation.

1 Like
4

If you don’t want to stick to a predefined size, you could use a schema like this …

julia> arr2=Vector{Int64}[]
Vector{Int64}[]

julia> push!(arr2,[])
1-element Vector{Vector{Int64}}:
 []

julia> push!(arr2,[])
2-element Vector{Vector{Int64}}:
 []
 []

julia> push!(arr2[2],33)
1-element Vector{Int64}:
 33

julia> push!(arr2[1],22)
1-element Vector{Int64}:
 22

julia> arr2
2-element Vector{Vector{Int64}}:
 [22]
 [33]

...

PS
I am not responsible for any adverse side effects

5

Btw this is going to have some pretty bad performances depending on what you actually want to do

6

Ah, thank you!