How to calculate column value based on hierarchy

Question

Lets say we agree on the following order in terms of hierarchy.

Baby --> Child --> Teenager --> Adult

I have this data set

           Name         Stage  Highest_Stage_Reached
0          Adam         Child  
1         Barry         Child
2           Ben         Adult
3          Adam      Teenager
4         Barry         Adult
5           Ben         Baby

How would I have the data set to populate the Highest_Stage_Reached field like this?

           Name         Stage  Highest_Stage_Reached
0          Adam         Child  Teenager
1         Barry         Child  Adult
2           Ben         Adult  Adult
3          Adam      Teenager  Teenager
4         Barry         Adult  Adult
5           Ben         Baby   Adult

Answer 1

You can use:

d={'Baby':0,'Child':1,'Teenager':2,'Adult':3}
df['rank']=df.Stage.map(d)
df['Highest_Stage_Reached']=df.groupby('Name')['rank'].transform('max').\
                                         map({v: k for k, v in d.items()})
print(df.drop('rank',1))

    Name     Stage Highest_Stage_Reached
0   Adam     Child              Teenager
1  Barry     Child                 Adult
2    Ben     Adult                 Adult
3   Adam  Teenager              Teenager
4  Barry     Adult                 Adult
5    Ben      Baby                 Adult

Answer 2

Convert the column to categorical, with order parameter. Now it lets you sort. This will also support variable number of arguments in Stage.

df['Stage'] = pd.Categorical(df['Stage'], ordered=True, categories=['Baby', 'Child','Teenager','Adult'])

df['Highest_Stage_Reached'] = df.groupby('Name').Stage.transform('max')

    Name    Stage       Highest_Stage_Reached
0   Adam    Child       Teenager
1   Barry   Child       Adult
2   Ben     Adult       Adult
3   Adam    Teenager    Teenager
4   Barry   Adult       Adult
5   Ben     Baby        Adult