Set upperbound in a column for a specific group by using Python

Question

I have a dataset given as such in Python:

#Load the required libraries
import pandas as pd


#Create dataset
data = {'ID': [1, 1, 1, 1, 1,1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 3, 3],
        'Salary': [1, 2, 3, 4, 5,6,7,8,9,10, 1, 2, 3,4,5,6, 1, 2, 3, 4,5,6,7,8],
        'Children': ['No', 'Yes', 'Yes', 'Yes', 'No','No', 'Yes', 'Yes', 'Yes', 'No', 'Yes', 'Yes', 'No', 'Yes', 'Yes', 'Yes', 'Yes', 'Yes', 'No', 'Yes', 'No', 'Yes', 'Yes', 'No'],
        'Days': [123, 128, 66, 120, 141,123, 128, 66, 120, 141, 52,96, 120, 141, 52,96, 120, 141,123,15,85,36,58,89],
        }

#Convert to dataframe
df = pd.DataFrame(data)
print("df = \n", df)

The above dataframe looks as such :

Now, for every ID/group, I wish to set an upperbound for some value of 'Salary'.

For example,

For ID=1, the upperbound of 'Salary' should be set at 4

For ID=2, the upperbound of 'Salary' should be set at 3

For ID=3, the upperbound of 'Salary' should be set at 5

The net result needs to look as such:

Can somebody please let me know how to achieve this task in python?

Answer 1

Use custom function with mapping by helper dictionary in GroupBy.transform:

d = {1:4, 2:3, 3:5}

def f(x):
    x.iloc[:d[x.name]] = d[x.name]
    return x

df['Salary'] = df.groupby('ID')['Salary'].transform(f)
print (df)
    ID  Salary Children  Days
0    1       4       No   123
1    1       4      Yes   128
2    1       4      Yes    66
3    1       4      Yes   120
4    1       5       No   141
5    1       6       No   123
6    1       7      Yes   128
7    1       8      Yes    66
8    1       9      Yes   120
9    1      10       No   141
10   2       3      Yes    52
11   2       3      Yes    96
12   2       3       No   120
13   2       4      Yes   141
14   2       5      Yes    52
15   2       6      Yes    96
16   3       5      Yes   120
17   3       5      Yes   141
18   3       5       No   123
19   3       5      Yes    15
20   3       5       No    85
21   3       6      Yes    36
22   3       7      Yes    58
23   3       8       No    89

Another idea is use GroupBy.cumcount for counter per ID, compared by mapped ID and if match set mapped Series by Series.mask:

d = {1:4, 2:3, 3:5}

s = df['ID'].map(d)
df['Salary'] = df['Salary'].mask(df.groupby('ID').cumcount().lt(s), s)

Or if counter column is in Salary is possible use:

s = df['ID'].map(d)
df['Salary'] = df['Salary'].mask(df['Salary'].le(s), s)

---

print (df)
    ID  Salary Children  Days
0    1       4       No   123
1    1       4      Yes   128
2    1       4      Yes    66
3    1       4      Yes   120
4    1       5       No   141
5    1       6       No   123
6    1       7      Yes   128
7    1       8      Yes    66
8    1       9      Yes   120
9    1      10       No   141
10   2       3      Yes    52
11   2       3      Yes    96
12   2       3       No   120
13   2       4      Yes   141
14   2       5      Yes    52
15   2       6      Yes    96
16   3       5      Yes   120
17   3       5      Yes   141
18   3       5       No   123
19   3       5      Yes    15
20   3       5       No    85
21   3       6      Yes    36
22   3       7      Yes    58
23   3       8       No    89