Return the max value in a new column for each repeating value in the other column

Background: I was hoping to generate a new column named: datasample based on another column named: end_bin from a table.

Question: Is there a way to return the max value in each row of the new column if the value is repeated in the previous column.

Expected result:

I couldnt find a method to do this in pandas, any help is appreciated:)

>Solution :

Your question is unclear, but it looks like you want the size per group:

df['datasample'] = df.groupby('end_bin')['end_bin'].transform('size')

Output:

   end_bin  datasample
0        6           1
1        8           1
2       10           1
3        2           3
4        3           1
5        2           3
6        2           3