# How to concatenate a 2d array to a 3d array
**URL:** https://discourse.julialang.org/t/how-to-concatenate-a-2d-array-to-a-3d-array/44713
**Category:** New to Julia
**Tags:** question
**Created:** [August 10, 2020, 9:53pm UTC](https://discourse.julialang.org/t/how-to-concatenate-a-2d-array-to-a-3d-array/44713 "2020-08-10T21:53:40Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@mkarikom](https://discourse.julialang.org/u/mkarikom)
#### Post date: [August 10, 2020, 9:53pm UTC](https://discourse.julialang.org/t/how-to-concatenate-a-2d-array-to-a-3d-array/44713/1 "2020-08-10T21:53:40Z")
Just trying to add an extra column to `check1` (which has 4 rows) for both layers of dim 3, so I figured I could just concatenate it with the 4x2 matrix `check2`.
MWE:
```julia
Random.seed!(1)
check1 = rand(4,3,2)
[:, :, 1] =
0.236033 0.488613 0.251662
0.346517 0.210968 0.986666
0.312707 0.951916 0.555751
0.00790928 0.999905 0.437108
[:, :, 2] =
0.424718 0.251379 0.0769509
0.773223 0.0203749 0.640396
0.28119 0.287702 0.873544
0.209472 0.859512 0.278582
check2 = rand(4,2)
4×2 Array{Float64,2}:
0.751313 0.0856352
0.644883 0.553206
0.0778264 0.46335
0.848185 0.185821
check3 = cat(check1,check2,dims=(1,3))
ERROR: DimensionMismatch("mismatch in dimension 2 (expected 3 got 2)")
```
What I was expecting:
```julia
4×3×2 Array{Float64,3}:
[:, :, 1] =
0.236033 0.488613 0.251662 0.751313
0.346517 0.210968 0.986666 0.644883
0.312707 0.951916 0.555751 0.0778264
0.00790928 0.999905 0.437108 0.848185
[:, :, 2] =
0.424718 0.251379 0.0769509 0.0856352
0.773223 0.0203749 0.640396 0.553206
0.28119 0.287702 0.873544 0.46335
0.209472 0.859512 0.278582 0.185821
```
Edit: corrected ‘expected `check3`’
---
### Author:  [@Henrique\_Becker](https://discourse.julialang.org/u/Henrique_Becker)
#### Post date: [August 10, 2020, 10:20pm UTC](https://discourse.julialang.org/t/how-to-concatenate-a-2d-array-to-a-3d-array/44713/2 "2020-08-10T22:20:17Z")
Put the two objects in the same shape, and then do a horizontal concatenate:
```julia
julia> hcat(check1, reshape(check2, 4, 1, 2))
4×4×2 Array{Float64,3}:
[:, :, 1] =
0.236033 0.488613 0.251662 0.751313
0.346517 0.210968 0.986666 0.644883
0.312707 0.951916 0.555751 0.0778264
0.00790928 0.999905 0.437108 0.848185
[:, :, 2] =
0.424718 0.251379 0.0769509 0.0856352
0.773223 0.0203749 0.640396 0.553206
0.28119 0.287702 0.873544 0.46335
0.209472 0.859512 0.278582 0.185821
```
This is not what you were expecting, but I do think you copy-pasted your expectations wrong, as the same column is used two times (and the other is not used).
---
### Author:  [@mkarikom](https://discourse.julialang.org/u/mkarikom)
#### Post date: [August 11, 2020, 12:52am UTC](https://discourse.julialang.org/t/how-to-concatenate-a-2d-array-to-a-3d-array/44713/3 "2020-08-11T00:52:52Z")
That works, thanks.
Yep the original post was wrong. I’ll correct it.