Python Question
python pandas conditional ranking
A1 1
A2 2
A3 1.5
B1 1
B2 -2
B3 2
B4 -1.5
Now I want a output of rank within each regex A*, B* etc.,
A1 1 3
A2 2 1
A3 1.5 2
B1 1 2
B2 -2 4
B3 2 1
B4 -1.5 3
How can I achieve this directly using pandas inbuilt functionalities as .rank gives only rank in entire set.
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Answer Source
You can use groupby by Series created by extract with rank:
print (df)
a b
0 A1 1.0
1 A2 2.0
2 A3 1.5
3 B1 1.0
4 B2 -2.0
5 B3 2.0
6 B4 -1.5
a = df.a.str.extract('([a-zA-Z])', expand=False)
print (a)
0 A
1 A
2 A
3 B
4 B
5 B
6 B
Name: a, dtype: object
df['c'] = df.groupby(a).b.rank(method='dense', ascending=False).astype(int)
print (df)
a b c
0 A1 1.0 3
1 A2 2.0 1
2 A3 1.5 2
3 B1 1.0 2
4 B2 -2.0 4
5 B3 2.0 1
6 B4 -1.5 3
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