提取数据框的索引，按列值分组

Question

I have a Pandas dataframe which is properly indexed:

    delta   y
0   0       10  
1   1       10
2   1       10
3   1       10
4   0       9
5   1       9

I want to extract the indices conditioned on one column (where delta = 1), but group them by the values of a different column (y). Ideally, I would like a dictionary of the following form:

{10 : [ 1, 2, 3], 9 : [ 5]}

Answer 1

Filter your df firstly , the we using groupby and to_dict

df[df.delta==1].reset_index().groupby('y').index.apply(list).to_dict()
Out[859]: {9: [5], 10: [1, 2, 3]}