Python Pandas 中每组的排名顺序
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Ranking order per group in Pandas
提问by Amelio Vazquez-Reina
Consider a dataframe with three columns: group_ID, item_IDand value. Say we have 10 itemIDstotal.
考虑一个包含三列的数据框：group_ID,item_ID和value。假设我们itemIDs总共有 10个。
I need to rank each item_ID(1 to 10) withineach group_IDbased on value, and then see the mean rank (and other stats) across groups (e.g. the IDs with the highestvalue across groups would get ranks closer to 1). How can I do this in
Pandas?
我需要每一个排名item_ID（1〜10）内各group_ID基础上value，再看到平均等级（和其它数据）跨群体（如用的ID最高的各组值会得到等级越接近1）。我怎样才能在 Pandas 中做到这一点？
This answerdoes something very close with qcut, but not exactly the same.
这个答案与 非常接近qcut，但并不完全相同。
A data example would look like:
数据示例如下所示：
group_ID item_ID value
0 0S00A1HZEy AB 10
1 0S00A1HZEy AY 4
2 0S00A1HZEy AC 35
3 0S03jpFRaC AY 90
4 0S03jpFRaC A5 3
5 0S03jpFRaC A3 10
6 0S03jpFRaC A2 8
7 0S03jpFRaC A4 9
8 0S03jpFRaC A6 2
9 0S03jpFRaC AX 0
which would result in:
这将导致：
group_ID item_ID rank
0 0S00A1HZEy AB 2
1 0S00A1HZEy AY 3
2 0S00A1HZEy AC 1
3 0S03jpFRaC AY 1
4 0S03jpFRaC A5 5
5 0S03jpFRaC A3 2
6 0S03jpFRaC A2 4
7 0S03jpFRaC A4 3
8 0S03jpFRaC A6 6
9 0S03jpFRaC AX 7
采纳答案by DSM
There are lots of different arguments you can pass to rank; it looks like you can use rank("dense", ascending=False)to get the results you want, after doing a groupby:
您可以传递许多不同的参数rank；rank("dense", ascending=False)在执行以下操作后，您似乎可以使用它来获得所需的结果groupby：
>>> df["rank"] = df.groupby("group_ID")["value"].rank("dense", ascending=False)
>>> df
group_ID item_ID value rank
0 0S00A1HZEy AB 10 2
1 0S00A1HZEy AY 4 3
2 0S00A1HZEy AC 35 1
3 0S03jpFRaS AY 90 1
4 0S03jpFRaS A5 3 5
5 0S03jpFRaS A3 10 2
6 0S03jpFRaS A2 8 4
7 0S03jpFRaS A4 9 3
8 0S03jpFRaS A6 2 6
9 0S03jpFRaS AX 0 7
But note that if you're not using a global ranking scheme, finding out the mean rank across groups isn't very meaningful-- unless there are duplicate values in a group (and so you have duplicate rank values) all you're doing is measuring how many elements there are in a group.
但请注意，如果您不使用全局排名方案，那么找出各组的平均排名并不是很有意义——除非您正在做的所有组中都有重复的值（因此您有重复的排名值）正在测量一个组中有多少个元素。
