dataframe - 如何让函数聚合 "ignore"列？

Question

假设我有一个包含多个分类维度和一个“值”维度的数据框，我想按其中一些维度进行聚合，而忽略其他维度。

在 Julia DataFrames 中有聚合函数，但如果我给出一些分类值，我会得到一个错误，因为它试图将函数(这里是求和)也应用于它们，而不是仅仅忽略它们:

在:

using DataArrays, DataFrames
df = DataFrame(
  colour = ["green","blue","white","green","green"],
  shape  = ["circle", "triangle", "square","square","circle"],
  border = ["dotted", "line", "line", "line", "dotted"],
  area   = [1.1, 2.3, 3.1, 4.2, 5.2])

输出:

    colour  shape       border  area
1   green   circle      dotted  1.1
2   blue    triangle    line    2.3
3   white   square      line    3.1
4   green   square      line    4.2
5   green   circle      dotted  5.2

在:

aggregate(df,[:colour,:shape, :border],sum) # Ok
aggregate(df,[:colour,:shape],sum) # what I would like, ignoring border column

输出:

LoadError: MethodError: no method matching +(::String, ::String)

显然我可能只是在聚合之前删除了额外的列，但也许有一种方法可以在单个段落中完成它？

Answer 1

来自 https://juliastats.github.io/DataFrames.jl/split_apply_combine/

by(df, [:colour,:shape]) do df
    DataFrame(m = sum(df[:area]))
end