How To Use .loc With Multiple Conditions And Groupby

I have a df thats grouped by 'Key'. I want to flag any row within a group where the discharge date matches another discharge date AND between those rows one of rows has a num1 valu

Solution 1:

You can accomplish that by using filter.

df.loc[df.groupby(['Key','discharge']).Num1.filter(lambda x : (x.isin(num1_range).any())&(len(x)>1)).index,'flag']=1
df
Out[317]: 
     Key  Num1  Num2      admit  discharge  flag
0  10003    12   121 2012-05-06 2012-05-08   1.0
1  10003    13   122 2012-05-08 2012-05-08   1.0
2  10003    13   122 2012-10-10 2012-10-12   NaN
3  10003    13   124 2012-10-10 2012-10-16   NaN
4  10003    12   125 2012-10-10 2012-10-23   NaN
5  10003    13   126 2012-11-10 2012-11-11   NaN
6  10034    16   127 2012-05-16 2012-05-20   NaN
7  10034    13   128 2012-05-20 2012-05-20   NaN