识别 pandas 数据框中的组之间的差异 [英] Identifying differences between groups in pandas dataframe
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问题描述
我有一个按日期和ID索引的熊猫数据框.我想:
I have a pandas dataframe indexed by date and and ID. I would like to:
- 确定日期之间添加和删除的ID
- 将ID和添加/删除日期一起添加到另一个数据框.
date ID value
12/31/2010 13 -0.124409
9 0.555959
1 -0.705634
2 -3.123603
4 0.725009
1/31/2011 13 0.471078
9 0.276006
1 -0.468463
22 1.076821
11 0.668599
所需的输出:
date ID flag
1/31/2011 22 addition
1/31/2011 11 addition
1/31/2011 2 deletion
1/31/2011 4 deletion
我尝试了在熊猫中两个数据框之间的差异 .我无法使它在分组的数据帧上工作.我不确定如何遍历每个组,并与上一个组进行比较.
I have tried Diff between two dataframes in pandas . I cannot get this to work on a grouped dataframe. I am unsure how to loop over each group, and compare to the previous group.
推荐答案
我创建了一个辅助函数,用于移动pandas.MultiIndex
的第一级.这样,我可以将其与原始索引进行区别,以确定添加和删除.
I created a helper function that shifts the first level of a pandas.MultiIndex
. With this, I can difference it with the original index to determine additions and deletions.
def shift_level(idx):
level = idx.levels[0]
mapping = dict(zip(level[:-1], level[1:]))
idx = idx.set_levels(level.map(mapping.get), 0)
return idx[idx.get_level_values(0).notna()].remove_unused_levels()
idx = df.index
fidx = shift_level(idx)
additions = fidx.difference(idx)
deletions = idx[idx.labels[0] > 0].difference(fidx)
pd.Series('+', additions).append(
pd.Series('-', deletions)).rename('flag').reset_index()
date ID flag
0 2011-01-31 2 +
1 2011-01-31 4 +
2 2011-01-31 11 -
3 2011-01-31 22 -
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