# Make broadcasted function return Matrix instead of Array of Arrays
**URL:** https://discourse.julialang.org/t/make-broadcasted-function-return-matrix-instead-of-array-of-arrays/55729
**Category:** General Usage
**Tags:** question
**Created:** [February 21, 2021, 5:49pm UTC](https://discourse.julialang.org/t/make-broadcasted-function-return-matrix-instead-of-array-of-arrays/55729 "2021-02-21T17:49:50Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@Uroc327](https://discourse.julialang.org/u/Uroc327)
#### Post date: [February 21, 2021, 5:49pm UTC](https://discourse.julialang.org/t/make-broadcasted-function-return-matrix-instead-of-array-of-arrays/55729/1 "2021-02-21T17:49:50Z")
I have a function returning a (fixed and known-length) array for some input:
```julia
function bitlevels(n, x)
l = reverse(digits(x, base=2))
[repeat([0], n - length(l)); l]
end
```
When broadcasting this function to a vector (e.g., `bitlevels.(5, [0, 2, 3, 5])`), I get an Array of Arrays instead of a Matrix.
I’d assume this has performance penalties due to pointer indirection, when those arrays become large. How can I change my implementation, so that a Matrix instead of an Array of Arrays is returned?
(Or is this actually a bad idea and I’m better off working on Arrays of Arrays?)
---
### Author:  [@jling](https://discourse.julialang.org/u/jling)
#### Post date: [February 21, 2021, 5:51pm UTC](https://discourse.julialang.org/t/make-broadcasted-function-return-matrix-instead-of-array-of-arrays/55729/2 "2021-02-21T17:51:52Z")
if your function returns a vector, then broadcasting (by construction) can only return a vector of vector. you either need to cat the resul manually, or you need to map reduce and cat along the way
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### Author:  [@Uroc327](https://discourse.julialang.org/u/Uroc327)
#### Post date: [February 21, 2021, 5:52pm UTC](https://discourse.julialang.org/t/make-broadcasted-function-return-matrix-instead-of-array-of-arrays/55729/3 "2021-02-21T17:52:49Z")
Okay, thanks. So I’ll check the performance, how copying to a matrix compares to working on arrays of arrays.