Access subdf in @by and @combine about dataframesmeta.jl HOT 7 CLOSED

What about

combine(gd) do sdf
    @with sdf begin
        :x1
     end
end

You have to repeat sdf twice, but you can get both the sdf and use the columns nicely.

from dataframesmeta.jl.

I don't think it would be possible to have something like the following

@by df :col1 begin
    :x1 # Column in df
    _subdf # reserved name for subdf
end

Since this is not possible in the src => fun => dest mini-language.

I think what you want is essentially

by(fun, df, groupcol) = combine(fun, groupby(df, groupcol))

I'm not sure this is worth it, but if so, it would belong in DataFrames.jl, not DataFramesMeta.jl, which is reserved for metaprogramming.

from dataframesmeta.jl.

What about an inner macro then?

@by df :col1 begin
    @withsubdf nrow(:x1)
end

to tell the outer macro that we want the :x1 column of the subdf and not that of the main df.

from dataframesmeta.jl.

That's currently pretty close to what's implemented, right?

@by df :col1 begin
    :y = f(:col2)
end

from dataframesmeta.jl.

This will apply f to the entire column of df, but not to the subdataframes created by groupby.
It is not equivalent to

combine(groupby(df, :col1)) do sdf
    f(sdf.col2)
end

which does apply f to the subdataframes.

from dataframesmeta.jl.

Nevermind, one can actually use length(:col2) to get the size of the df. We still cannot work with the subdf, unlike the DataFrame do syntax, but the applications are not that numerous.

from dataframesmeta.jl.

Yes that's fairly clean. No need for a dedicated macro with this syntax in my opinion. Thank you.

from dataframesmeta.jl.