Pandas increment counter on condition

user_11951277 0
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suppose the following DataFrame is given:

df

   step    
0  1.0  
1  1.0  
2  1.0  
3  2.0  
4  2.0  
5  3.0  
6  4.0
7  1.0
8  1.0
9  2.0
10 3.0

I now want to "cluster" the data based on the occurency of step==1.0 and increment a counter if that condition is met.

Desired outcome is:

df_count

   step   count
0  1.0    1
1  1.0    1  
2  1.0    1  
3  2.0    1  
4  2.0    1  
5  3.0    1  
6  4.0    1
7  1.0    2
8  1.0    2
9  2.0    2
10 3.0    2

Can you come up with any pandas pipeline do achieve this? Thanks in advance

pandas dataframe python
1 Answers

You can test 1 values and also first consecutives, last add cumulative sum for counter:

df['new'] = (df['step'].eq(1.0) & df['step'].ne(df['step'].shift())).cumsum()

print (df)
    step  new
0    1.0    1
1    1.0    1
2    1.0    1
3    2.0    1
4    2.0    1
5    3.0    1
6    4.0    1
7    1.0    2
8    1.0    2
9    2.0    2
10   3.0    2
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