How to reset row value in pandas

How to reset row value in pandas - Printable Version

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How to reset row value in pandas - Mekala - Sep-19-2020

Hi,
I have below dataframe:

df

ID   Grp subGrp Rank  SNO
A.1  A.0  A     S      1
A.2  A.0  A     S      1
A.2  A.0  A     N      1
A.6  A.0  A     N      1
A.3  A.0  A     S      1 
A.1  A.B  A     3      1
A.2  A.B  A     3      1
A.4  A.0  A     3      1
A.2  A.0  A     3      1

Now I want to increase SNO by 1 in each row, but reset at each repeating ID(at first repeat row) & same columns "subGrp" &"Rank"

Desired output:

ID Grp subGrp Rank SNO
A.1 A.0 A S 1
A.2 A.0 A S 2
A.2 A.0 A S 1
A.6 A.0 A S 2
A.3 A.0 A S 3
A.1 A.0 A S 1
A.2 A.0 A S 2
A.4 A.0 A S 3
A.2 A.0 A S 1
A.1 A.0 A S 2

A.1 rpeats & A.2 repeats but its coninuouse so not reset at A.2. A.2 rpeats again 8th row, reset and increase by one next row.