demean

de.jl

julia> using DataFrames, DataFramesMeta, Lazy

julia> df = DataFrame(id=[1,1,1,2,2,2,3,3,3],x=rand(9))
9x2 DataFrame
| Row | id | x         |
|-----|----|-----------|
| 1   | 1  | 0.0470736 |
| 2   | 1  | 0.440199  |
| 3   | 1  | 0.156013  |
| 4   | 2  | 0.864873  |
| 5   | 2  | 0.236155  |
| 6   | 2  | 0.851055  |
| 7   | 3  | 0.672592  |
| 8   | 3  | 0.30145   |
| 9   | 3  | 0.987773  |

julia> @> df @by(:id,demeanx = :x .- mean(:x))
9x2 DataFrame
| Row | id | demeanx    |
|-----|----|------------|
| 1   | 1  | -0.167355  |
| 2   | 1  | 0.225771   |
| 3   | 1  | -0.0584158 |
| 4   | 2  | 0.214178   |
| 5   | 2  | -0.414539  |
| 6   | 2  | 0.200361   |
| 7   | 3  | 0.0186536  |
| 8   | 3  | -0.352488  |
| 9   | 3  | 0.333835   |