# Specify AsTable output column names
**URL:** https://discourse.julialang.org/t/specify-astable-output-column-names/72742
**Category:** Data
**Tags:** dataframes
**Created:** [December 8, 2021, 4:21am UTC](https://discourse.julialang.org/t/specify-astable-output-column-names/72742 "2021-12-08T04:21:21Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@jzr](https://discourse.julialang.org/u/jzr)
#### Post date: [December 8, 2021, 4:21am UTC](https://discourse.julialang.org/t/specify-astable-output-column-names/72742/1 "2021-12-08T04:21:21Z")
Can I specify the name of the output column?
```julia
using DataFrames, Chain
@chain DataFrame(a=[1,2,3,1,2,3], b=[:x, :y, :z, :x, :y, :x]) begin
groupby(:a)
combine(:b=>unique=>:b, :b => (b->mean.(map(b₀->b₀.==b, unique(b)))) => AsTable)
end
4×3 DataFrame
Row │ a b x1
│ Int64 Symbol Float64
─────┼────────────────────────
1 │ 1 x 1.0
2 │ 2 y 1.0
3 │ 3 z 0.5
4 │ 3 x 0.5
```
---
### Author:  [@sijo](https://discourse.julialang.org/u/sijo)
#### Post date: [December 8, 2021, 7:11am UTC](https://discourse.julialang.org/t/specify-astable-output-column-names/72742/2 "2021-12-08T07:11:31Z")
Yes you just need to return a “table” with column names.
With a named tuple:
```julia
combine(:b=>unique=>:b, :b => (b->(; c=mean.(map(b₀->b₀.==b, unique(b))))) => AsTable)
```
With a Dict:
```julia
combine(:b=>unique=>:b, :b => (b->Dict(:c=>mean.(map(b₀->b₀.==b, unique(b))))) => AsTable)
```
---
### Author:  [@bkamins](https://discourse.julialang.org/u/bkamins)
#### Post date: [December 8, 2021, 7:31am UTC](https://discourse.julialang.org/t/specify-astable-output-column-names/72742/3 "2021-12-08T07:31:53Z")
Additionally in this case just the following works:
```julia
julia> @chain DataFrame(a=[1,2,3,1,2,3], b=[:x, :y, :z, :x, :y, :x]) begin
groupby(:a)
combine(:b=>unique=>:b, :b => (b->mean.(map(b₀->b₀.==b, unique(b)))) => :output)
end
4×3 DataFrame
Row │ a b output
│ Int64 Symbol Float64
─────┼────────────────────────
1 │ 1 x 1.0
2 │ 2 y 1.0
3 │ 3 z 0.5
4 │ 3 x 0.5
```
or - if indeed you produce a table and want to give new names for its columns use:
```julia
julia> @chain DataFrame(a=[1,2,3,1,2,3], b=[:x, :y, :z, :x, :y, :x]) begin
groupby(:a)
combine(:b=>unique=>:b, :b => (b->mean.(map(b₀->b₀.==b, unique(b)))) => [:output])
end
4×3 DataFrame
Row │ a b output
│ Int64 Symbol Float64
─────┼────────────────────────
1 │ 1 x 1.0
2 │ 2 y 1.0
3 │ 3 z 0.5
4 │ 3 x 0.5
```
(the latter is more useful if you had more than one column - for a single vector the former is sufficient)
What @sijo proposed is a general solution if you want `AsTable` as a target and want to specify the column names within a transformation function.