# Slicing and merging of CartesianIndices
**URL:** https://discourse.julialang.org/t/slicing-and-merging-of-cartesianindices/61519
**Category:** General Usage
**Tags:** indexing
**Created:** [May 20, 2021, 1:55pm UTC](https://discourse.julialang.org/t/slicing-and-merging-of-cartesianindices/61519 "2021-05-20T13:55:11Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@fedoroff](https://discourse.julialang.org/u/fedoroff)
#### Post date: [May 20, 2021, 1:55pm UTC](https://discourse.julialang.org/t/slicing-and-merging-of-cartesianindices/61519/1 "2021-05-20T13:55:11Z")
Hello,
Let’s assume I have a two-dimensional array and the list of Cartesian indices which allow me to extract some subset of the array elements:
```julia
A = zeros((6, 9))
ci = CartesianIndices((2:2:6, 3:3:9))
A[ci]
```
Now, having `ci`, how I can extract the Cartesian indices which correspond separately to the first and second dimensions of the array? If I will define them manually, they will be
```julia
ci1 = CartesianIndices((2:2:6,))
ci2 = CartesianIndices((3:3:9,))
A[ci1, :]
A[:, ci2]
```
And the other way around, having `ci1` and `ci2`, how I can merge them into the original `ci`?
The last question is related to my earlier post [https://discourse.julialang.org/t/combine-cartesianindices-for-effective-cuda-kernels/](https://discourse.julialang.org/t/combine-cartesianindices-for-effective-cuda-kernels/)
Thank you.
---
### Author:  [@sijo](https://discourse.julialang.org/u/sijo)
#### Post date: [May 20, 2021, 4:15pm UTC](https://discourse.julialang.org/t/slicing-and-merging-of-cartesianindices/61519/2 "2021-05-20T16:15:14Z")
You can do use `ci.indices` though I think that’s an undocumented internal:
```julia
ci1 = CartesianIndices(ci.indices[1])
ci2 = CartesianIndices(ci.indices[2])
```
You can get the same information with `first(ci)`, `step(ci)`, `last(ci)` but that’s less convenient.
To recover the full list:
```julia
CartesianIndices((ci1.indices[1], ci2.indices[1]))
```
Another idea using arrays of `CartesianIndex` rather than `CartesianIndices`:
```julia
julia> i1 = getindex.(ci[:, 1], 1)
3-element Vector{Int64}:
2
4
6
julia> i2 = getindex.(ci[1, :], 2)
3-element Vector{Int64}:
3
6
9
julia> CartesianIndex.(i1, i2')
3×3 Matrix{CartesianIndex{2}}:
CartesianIndex(2, 3) CartesianIndex(2, 6) CartesianIndex(2, 9)
CartesianIndex(4, 3) CartesianIndex(4, 6) CartesianIndex(4, 9)
CartesianIndex(6, 3) CartesianIndex(6, 6) CartesianIndex(6, 9)
```
---
### Author:  [@fedoroff](https://discourse.julialang.org/u/fedoroff)
#### Post date: [May 20, 2021, 4:28pm UTC](https://discourse.julialang.org/t/slicing-and-merging-of-cartesianindices/61519/3 "2021-05-20T16:28:56Z")
Thank you.
`indices` is exactly what I need.