# Groupby() on two individual arrays

**URL:** <https://discourse.julialang.org/t/groupby-on-two-individual-arrays/59643>\
**Category:** General Usage\
**Tags:** question, array\
**Created:** [April 20, 2021, 7:12am UTC](https://discourse.julialang.org/t/groupby-on-two-individual-arrays/59643 "2021-04-20T07:12:39Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![mdsa3d](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/mdsa3d/32/20389_2.png) [@mdsa3d](https://discourse.julialang.org/u/mdsa3d)\
**Post date:** [April 20, 2021, 7:12am UTC](https://discourse.julialang.org/t/groupby-on-two-individual-arrays/59643/1 "2021-04-20T07:12:39Z")

</div>

I have two arrays with same dimension:

```julia
a1 = [1,1,3,4,6,6]
a2 = [1,2,3,4,5,6]

```

But I want to group both of them with respect to array `a1` and get the mean of the array `a2` for each group.  
My output is coming from array `a2`, as mentioned below:

```julia
result:
1.5
3.0
4.0
5.5

```

Please suggest an approach to achieve this task.  
Thanks!!

---

<div class="post-metadata">

**Author:** ![bkamins](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/bkamins/32/208538_2.png) [@bkamins](https://discourse.julialang.org/u/bkamins)\
**Post date:** [April 20, 2021, 7:55am UTC](https://discourse.julialang.org/t/groupby-on-two-individual-arrays/59643/2 "2021-04-20T07:55:18Z")

</div>

[https://stackoverflow.com/questions/67174230/groupby-using-two-arrays-in-julia/67174276](https://stackoverflow.com/questions/67174230/groupby-using-two-arrays-in-julia/67174276)