# How to compute the correlation between elements in an array of arrays?
**URL:** https://discourse.julialang.org/t/how-to-compute-the-correlation-between-elements-in-an-array-of-arrays/35763
**Category:** New to Julia
**Tags:** question
**Created:** [March 9, 2020, 6:04pm UTC](https://discourse.julialang.org/t/how-to-compute-the-correlation-between-elements-in-an-array-of-arrays/35763 "2020-03-09T18:04:21Z")
**Posts on this page:** 5
**Page:** 1
### Author:  [@zxjroger](https://discourse.julialang.org/u/zxjroger)
#### Post date: [March 9, 2020, 6:04pm UTC](https://discourse.julialang.org/t/how-to-compute-the-correlation-between-elements-in-an-array-of-arrays/35763/1 "2020-03-09T18:04:21Z")
Suppose that I have the following array of vectors.
```julia
temp = Matrix{Vector{Float64}}(undef, 3, 1000)
for i = 1:3
for j = 1:1000
temp[i,j] = rand(10)
end
end
```
Now I want to compute the correlation between the first element in the inner-vector and the second element in the inner-vector, separately for each row dimension of the outer-matrix. I was trying to do something like this:
```julia
cor(temp[1,:][1,:], temp[1,:][2,:])
```
But `temp[1,:][1,:]` only gives me the first vector , rather then collecting horizontally the first elements in all vectors in the first row of the outer-matrix.
---
### Author:  [@stillyslalom](https://discourse.julialang.org/u/stillyslalom)
#### Post date: [March 9, 2020, 6:43pm UTC](https://discourse.julialang.org/t/how-to-compute-the-correlation-between-elements-in-an-array-of-arrays/35763/2 "2020-03-09T18:43:00Z")
You can define your own slicing function
```julia
julia> AoV_row(arr, row, idx) = getindex.(arr[row, :], idx)
AoV_row (generic function with 1 method)
julia> cor(AoV_row(temp,1,1), AoV_row(temp,1,2))
0.0036541528935823526
```
---
### Author:  [@zxjroger](https://discourse.julialang.org/u/zxjroger)
#### Post date: [March 9, 2020, 11:08pm UTC](https://discourse.julialang.org/t/how-to-compute-the-correlation-between-elements-in-an-array-of-arrays/35763/3 "2020-03-09T23:08:22Z")
Wow, this is much better than my for loop code. So, there is no direct way say `temp[i,j]` to do it. Thank you.
---
### Author:  [@GunnarFarneback](https://discourse.julialang.org/u/GunnarFarneback)
#### Post date: [March 10, 2020, 6:38am UTC](https://discourse.julialang.org/t/how-to-compute-the-correlation-between-elements-in-an-array-of-arrays/35763/4 "2020-03-10T06:38:58Z")
If you want slicing to be more convenient you would be better off with a 3-dimensional array than a matrix of vectors.
---
### Author:  [@zxjroger](https://discourse.julialang.org/u/zxjroger)
#### Post date: [March 10, 2020, 5:15pm UTC](https://discourse.julialang.org/t/how-to-compute-the-correlation-between-elements-in-an-array-of-arrays/35763/5 "2020-03-10T17:15:53Z")
Thanks, I will also think about it.