5.6 Data Summaries
Similar to the combine DataFrames.jl function (Section 4.8), DataFramesMeta.jl has a @combine macro.
@combine leftjoined :mean_grade_2020 = mean(:grade_2020)| mean_grade_2020 |
|---|
| 4.625 |
@combine also supports multiple operations inside a begin ... end statement:
@combine leftjoined begin
:mean_grade_2020 = mean(:grade_2020)
:mean_grade_2021 = mean(:grade_2021)
end| mean_grade_2020 | mean_grade_2021 |
|---|---|
| 4.625 | 6.375 |
Most of the time we would use @combine in a grouped dataframe by pairing it with groupby:
gdf = groupby(leftjoined, :name)
@combine gdf begin
:mean_grade_2020 = mean(:grade_2020)
:mean_grade_2021 = mean(:grade_2021)
end| name | mean_grade_2020 | mean_grade_2021 |
|---|---|---|
| Sally | 1.0 | 9.5 |
| Hank | 4.0 | 6.0 |
| Bob | 5.0 | 5.0 |
| Alice | 8.5 | 5.0 |
