transform Count consecutive integers

Question

i have a dataset like

id
1
2
3
4
7
8

i want my output as:

id   count
1     4
2     4
3     4
4     4
7     2
8     2

Thanks in advance

Answer 1

Create Series for consecutive integers by Series.diff , compare for not equal 1 by Series.ne and add cumulative sum by Series.cumsum :

s = df['id'].diff().ne(1).cumsum()

Then use Series.map with Series.value_counts :

df['count'] = s.map(s.value_counts())

Or GroupBy.transform with GroupBy.size :

df['count'] = s.groupby(s).transform('size') 

print (df)
   id  count
0   1      4
1   2      4
2   3      4
3   4      4
4   7      2
5   8      2