# Storing output in matrix or vector format
**URL:** https://discourse.julialang.org/t/storing-output-in-matrix-or-vector-format/123207
**Category:** New to Julia
**Tags:** question
**Created:** [November 28, 2024, 10:32am UTC](https://discourse.julialang.org/t/storing-output-in-matrix-or-vector-format/123207 "2024-11-28T10:32:39Z")
**Posts on this page:** 5
**Page:** 1
### Author:  [@danieleavitabile](https://discourse.julialang.org/u/danieleavitabile)
#### Post date: [November 28, 2024, 10:32am UTC](https://discourse.julialang.org/t/storing-output-in-matrix-or-vector-format/123207/1 "2024-11-28T10:32:39Z")
I’m new to Julia, coming from Matlab. Consider the following sketched function
```julia
function time_stepper(f,u0,nsteps, ...)
# Allocate arrays
t = zeros(nsteps)
p = length(u0)
u = zeros(p,nsteps +1)
# Initialise
t[1] = 0.0
u[:,1] = u0
# update solution and update u, t
return t, u
```
While it’s clear that ` t` is a Vector, u may be a vector or a matrix, depending on `u0`. When p = 1, the code now returns a 1-column matrix, as opposed to a vector. Note I’ve used column-major structure for u, hoping this is good practice in Julia
What should I do to get a more idiomatic Julia code? What’s an appropriate data structure for `u` here?
---
### Author:  [@DNF](https://discourse.julialang.org/u/DNF)
#### Post date: [November 28, 2024, 10:50am UTC](https://discourse.julialang.org/t/storing-output-in-matrix-or-vector-format/123207/2 "2024-11-28T10:50:56Z")
Welcome from Matlab!
Your code is type stable regardless of the length of `u0`, it always returns a `Matrix`, which is p\times N if `u0` is a vector of length p (and if it’s 1\times N that would be similar to a _row_ vector.)
Now, if `u0` is a scalar instead of a length-1 vector, your code will fail with an error. In order to work for that situation too, you should add a dot to this expression: `u[:, 1] .= u0`, then it will work and be type stable in both cases.
If this is not your question, could you elaborate a bit more, for example giving two different example inputs with desired outputs?
(Then a small nitpick: Matlab doesn’t always force you to close a function definition with an `end`, but it is required in Julia. If you don’t do that, you will get errors or weird results.)
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### Author:  [@danieleavitabile](https://discourse.julialang.org/u/danieleavitabile)
#### Post date: [November 28, 2024, 11:02am UTC](https://discourse.julialang.org/t/storing-output-in-matrix-or-vector-format/123207/3 "2024-11-28T11:02:43Z")
Thanks @DNF, in fact, I threw ` u[:,1] .= u0` in the full code (and an end, but thanks for pointing this out!).
I’m wondering though if this is good Julia practice? I see that DifferentialEquation.jl, for instance, does not return a matrix for its output in a time stepper, but rather a vector of vectors? I don’t know if this makes sense, and thanks again
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### Author:  [@GunnarFarneback](https://discourse.julialang.org/u/GunnarFarneback)
#### Post date: [November 28, 2024, 11:19am UTC](https://discourse.julialang.org/t/storing-output-in-matrix-or-vector-format/123207/4 "2024-11-28T11:19:35Z")
Generally speaking, both a vector of vectors and the corresponding matrix can be good practice, depending on how it’s used and the performance characteristics of relevant operations.
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### Author:  [@danieleavitabile](https://discourse.julialang.org/u/danieleavitabile)
#### Post date: [November 28, 2024, 11:20am UTC](https://discourse.julialang.org/t/storing-output-in-matrix-or-vector-format/123207/5 "2024-11-28T11:20:55Z")
Thanks