# DataFrame: New columns with names from existing column

**URL:** https://discourse.julialang.org/t/dataframe-new-columns-with-names-from-existing-column/102658
**Category:** General Usage
**Tags:** question, dataframes
**Created:** [August 10, 2023, 1:41am UTC](https://discourse.julialang.org/t/dataframe-new-columns-with-names-from-existing-column/102658 "2023-08-10T01:41:25Z")
**Posts on this page:** 2
**Page:** 1

<div class="post-metadata">

### Author: ![bmit](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/bmit/32/12443_2.png) [@bmit](https://discourse.julialang.org/u/bmit)
#### Post date: [August 10, 2023, 1:41am UTC](https://discourse.julialang.org/t/dataframe-new-columns-with-names-from-existing-column/102658/1 "2023-08-10T01:41:25Z")

</div>

I’m trying to take an existing DataFrame that looks something like the following:

```julia
df = DataFrame(:x => [1, 2, 3, 1, 2], :y => [:A, :A, :A, :B, :B], :z => 1:2:9)

```

```julia
5×3 DataFrame
 Row │ x y z     
     │ Int64 Symbol Int64 
─────┼──────────────────────
   1 │ 1 A 1
   2 │ 2 A 3
   3 │ 3 A 5
   4 │ 1 B 7
   5 │ 2 B 9

```

and create a new one by 1) grouping by the values in column `:y`, 2) joining on the repeated values in `:x` and 3) creating multiple `:z` columns with new names pulled from `:y` groups. To illustrate, the output would look like

```julia
3×3 DataFrame
 Row │ x A B       
     │ Int64 Int64 Int64?  
─────┼───────────────────────
   1 │ 1 1 7
   2 │ 2 3 9
   3 │ 3 5 missing 

```

I’ve tried a few different approaches with `groupby` and `outerjoin` but haven’t found the right one yet. This is the closest I’ve gotten

```julia
outerjoin(groupby(df, :y)..., on=:x, makeunique=true)

```

```julia
3×5 DataFrame
 Row │ x y z y_1 z_1     
     │ Int64 Symbol? Int64? Symbol? Int64?  
─────┼──────────────────────────────────────────
   1 │ 1 A 1 B 7
   2 │ 2 A 3 B 9
   3 │ 3 A 5 missing missing 

```

---

<div class="post-metadata">

### Author: ![Dan](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/dan/32/42581_2.png) [@Dan](https://discourse.julialang.org/u/Dan)
#### Post date: [August 10, 2023, 1:50am UTC](https://discourse.julialang.org/t/dataframe-new-columns-with-names-from-existing-column/102658/2 "2023-08-10T01:50:55Z")

</div>

```julia
julia> unstack(df, :x, :y, :z)
3×3 DataFrame
 Row │ x A B       
     │ Int64 Int64? Int64?  
─────┼────────────────────────
   1 │ 1 1 7
   2 │ 2 3 9
   3 │ 3 5 missing

```

see `unstack` help for more explanations (this is good for doing pivot like operations from the spreadsheets world).