python - 获取数据框中每个用户发生类别更改的日期

Question

我正在使用 Pandas ==1.2.1
雷:

x = pd.DataFrame({"date":["20201211", "20201211", "20201212", "20201222", "20201222","20201223",
                          "20201211", "20201211", "20201212", "20201222", "20201222"],
                  "userid":["A", "A", "A", "A", "A", "A","B", "B", "B", "B", "B"],
                  "category":[1,1,2,2,2,1, 33, 33, 33, 34, 34]})

看起来像这样:

    date    userid  category
0   20201211    A   1
1   20201211    A   1
2   20201212    A   2
3   20201222    A   2
4   20201222    A   2
5   20201223    A   1
6   20201211    B   33
7   20201211    B   33
8   20201212    B   33
9   20201222    B   34
10  20201222    B   34

我想要做的是获取每个用户的类别更改时的日期
所以所需的数据框应该是这样的:

user         cat_changed             changed_cat
  A      [20201212, 20201223]         [2, 1]
  B          [20201222]                [34]

我试过按用户名、类别、日期分组，但从那里卡住了......

Answer 1

您可以先使用 diff() 获取过渡点。在 category ，然后将这些转换和聚合索引为 list :

>>> transitions = x.groupby('userid').category.diff().fillna(0).ne(0)
>>> x[transitions].groupby('userid').agg(list)

                          date  category
userid
     A    [20201212, 20201223]    [2, 1]
     B              [20201222]      [34]