问题
I am getting familiar with Julia Dataframes module. One thing that I haven't found a way yet to do is how to assign programmatically a custom column name of the result of a by() operation.
So for example I have no problem doing the following :
df = DataFrame(grp = rand(["a","b"], 100), x= rand(100), y = rand(100), z=rand(100))
by(df, :grp,result=(:x, :z)=>((x, y),) -> cov(x, y))
Giving the following dataframe
2×2 DataFrame
│ Row │ grp │ result │
│ │ String │ Float64 │
├─────┼────────┼─────────────┤
│ 1 │ b │ -0.00622699 │
│ 2 │ a │ -0.0303828 │
Now I would like the naming of the result to be dependent on some other part of my code. So i am trying things along this
resultColName="resultBis"
by(df, :grp,resultColName=(:x, :z)=>((x, y),) -> cov(x, y))
which gives me the following
2×2 DataFrame
│ Row │ grp │ resultColName │
│ │ String │ Float64 │
├─────┼────────┼───────────────┤
│ 1 │ b │ -0.00622699 │
│ 2 │ a │ -0.0303828 │
Which doesn't work as I want the result column to be named 'resultBis'. I understand why this happens, but is there currently a way to provide a string to chose the custom name of the result column ?
I imagine using macro could be one way to handle that and I would welcome that as an answer, but ideally I would like to do it directly within the DataFrames.jl. Any help is welcome. Thanks
回答1:
julia> by(df, :grp, (; Symbol(resultColName)=>(:x, :z)=>((x, y),) -> cov(x, y)))
2×2 DataFrame
│ Row │ grp │ resultBis │
│ │ String │ Float64 │
├─────┼────────┼────────────┤
│ 1 │ a │ -0.0110717 │
│ 2 │ b │ 0.0102181 │
Explanation:
by accepts a NamedTuple as the third parameter.
In order to create it programmatically we use the (; :key => value) operator. For more information type ?NamedTuple into the Julia console.
来源：https://stackoverflow.com/questions/60229490/julia-dataframe-how-to-use-string-for-custom-output-column-naming-in-by