pandas :groupby列出 [英] Pandas: groupby to list

问题描述

我有如下数据:

id  value   time

1   5   2000
1   6   2000
1   7   2000
1   5   2001
2   3   2000
2   3   2001
2   4   2005
2   5   2005
3   3   2000
3   6   2005

我的最终目标是将数据包含在以下列表中:

My final goal is to have data in a list like below:

[[5,6,7],[5]] (this is for id 1 grouped by the id and year)
[[3],[3],[4,5]] (this is for id 2 grouped by the id and year)
[[3],[6]] (same logic as above)

我已经使用df.groupby(['id', 'year'])对数据进行了分组.但是之后，我将无法访问组并以上述格式获取数据.

I have grouped the data using df.groupby(['id', 'year']). But after that, I am not able to access the groups and get the data in the above format.

推荐答案

您可以使用apply(list):

>>> df.groupby(['id', 'time'])['value'].apply(list)

id  time
1   2000    [5, 6, 7]
    2001          [5]
2   2000          [3]
    2001          [3]
    2005       [4, 5]
3   2000          [3]
    2005          [6]
Name: value, dtype: object

如果您确实希望使用与显示的格式完全相同的格式，则可以对id进行分组并再次应用list ，但这效率不高，而且这种格式可以说很难与...一起工作

If you really want it in the exact format as you displayed, you can then groupby id and apply list again, but this is not efficient, and that format is arguably harder to work with...

>>> df.groupby(['id','time'])['value'].apply(list).groupby('id').apply(list).tolist()
[[[5, 6, 7], [5]], [[3], [3], [4, 5]], [[3], [6]]]

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