# Unstack via group\_vg;map

**URL:** https://discourse.julialang.org/t/unstack-via-group-vg-map/130247
**Category:** General Usage
**Created:** [June 26, 2025, 5:04pm UTC](https://discourse.julialang.org/t/unstack-via-group-vg-map/130247 "2025-06-26T17:04:23Z")
**Posts on this page:** 2
**Page:** 1

<div class="post-metadata">

### Author: ![jar1](https://avatars.discourse-cdn.com/v4/letter/j/c0e974/32.png) [@jar1](https://discourse.julialang.org/u/jar1)
#### Post date: [June 26, 2025, 5:04pm UTC](https://discourse.julialang.org/t/unstack-via-group-vg-map/130247/1 "2025-06-26T17:04:23Z")

</div>

```julia
using DataManipulation, StructArrays, PrettyTables
julia> let d = StructArray(a=[1,1,2,2], b=[:x, :y, :x, :y], c=[10, 20, 30, 40])
           pretty_table(d)
           @p begin
               d
               group_vg((;_.a,))
               map((;key(_)..., (_.b .=> _.c)...))
               pretty_table
           end
       end
┌───────┬────────┬───────┐
│ a │ b │ c │
│ Int64 │ Symbol │ Int64 │
├───────┼────────┼───────┤
│ 1 │ x │ 10 │
│ 1 │ y │ 20 │
│ 2 │ x │ 30 │
│ 2 │ y │ 40 │
└───────┴────────┴───────┘
┌───────┬───────┬───────┐
│ a │ x │ y │
│ Int64 │ Int64 │ Int64 │
├───────┼───────┼───────┤
│ 1 │ 10 │ 20 │
│ 2 │ 30 │ 40 │
└───────┴───────┴───────┘

```

Is there a nicer approach to table `unstack`?

Elements a little less elegant than I’d like:

- the key `...` splat
- the `.=>` broadcast
- the pairs `...` splat

cc @aplavin

---

<div class="post-metadata">

### Author: ![aplavin](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/aplavin/32/222056_2.png) [@aplavin](https://discourse.julialang.org/u/aplavin)
#### Post date: [June 30, 2025, 10:06am UTC](https://discourse.julialang.org/t/unstack-via-group-vg-map/130247/2 "2025-06-30T10:06:17Z")

</div>

I think this pipeline you wrote is quite reasonable, especially splatting `key(_)...` is generally common thing to do. What is a bit tricky, is if you have different number of rows in each group and want to keep type stability… I thought about better ways for this operation a few times, but never really for long – personally for me, it comes up very rarely.

Typically, I find it natural to aggregate/process each group immediately, without materializing the full longer table. Or store values from each group in a data structure, either an array or a dict in this case:

```julia
@p let
	StructArray(a=[1,1,2,2], b=[:x, :y, :x, :y], c=[10, 20, 30, 40])
	@aside pretty_table()
	group_vg((;_.a,))
	map((;key(_)..., vals=Dict(_.b .=> _.c)))
end

```