Pandas: How to add a new column of Group ID to a dataframe based on the loop of a column of index sequence

Question

I have a dataframe like this :

Index	Column1	Column2
0	xxxxxxx	yyyy
1	xxxxxx	yyy
2	xxxxx	yy
0	xxx	y
1	xx	yyyyy

What I want is to add a new column to represent Group ID based on the loop of column Index. A new Group ID is required when Index resets to 0.

like this:

Index	Column1	Column2	Group ID
0	xxxxxxx	yyyy	1
1	xxxxxx	yyy	1
2	xxxxx	yy	1
0	xxx	y	2
1	xx	yyyyy	2

Please give me instructions, thanks

Answer 1

As you mentioned:

represent Group ID based on the loop of Index

If you mean that a new group is formed whenever Index reset to 0, you can try:

df['Group ID'] = df['Index'].eq(0).cumsum()

Or, if you mean a new group is formed whenever Index stop from an increasing sequence and starts from an index value smaller than the previous index, you can use:

df['Group ID'] = df['Index'].diff().lt(0).cumsum() + 1

Result:

print(df)

   Index  Column1 Column2  Group ID
0      0  xxxxxxx    yyyy         1
1      1   xxxxxx     yyy         1
2      2    xxxxx      yy         1
3      0      xxx       y         2
4      1       xx   yyyyy         2