python - 来自 Pandas 的 groupby 是可交换的吗？

Question

我想知道是否选择了以下行:

groupby(['a', 'b']) 

与通过以下方式选择的行相同:

groupby(['b', 'a'])

在这种情况下，行的顺序无关紧要。

有没有 groupby的情况不满足交换性？

Answer 1

每 definition以及使用 groupby 时应用的逻辑在 pandas ，它总是可交换的:

A groupby operation involves some combination of splitting the object, applying a function, and combining the results.

这种组合是线性的，因此是可交换的。重要的是，当传递多个 by 时值，在处理它们时应牢记新索引值的顺序。

来自维基百科的 linear combination和 commutative property :

In mathematics, a linear combination is an expression constructed from a set of terms by multiplying each term by a constant and adding the results. The idea that simple operations, such as the multiplication and addition of numbers, are commutative was for many years implicitly assumed.