How do I add a column to a pandas dataframe which has the highest value in a range but applying it to every row? [duplicate]

Question

I have the following code:

import pandas as pd
import numpy as np

df = pd.DataFrame([['red', 1], ['red', 13], ['red', 1], ['blue', 1], ['red', 112], ['blue', 10]])

df.columns = ["colour","rank"]

# df['highest_rank'] = ...

print(df)

"""
  colour  rank  highest_rank
0    red     1     122
1    red    13     122
2    red     1     122
3   blue     1     10
4    red   112     122
5   blue    10     10
"""

Hopefully, the example can show you what I'm trying to do as I'm struggling to describe what I'm wanting - The highest ranking of each colour.

wwnde · Accepted Answer · 2022-01-10 20:39:20Z

2

groupby colour and broadcast the highest rank in each group using transform. Code below

df['highest_rank']=df.groupby('colour')['rank'].transform('max')




colour  rank  highest_rank
0    red     1           112
1    red    13           112
2    red     1           112
3   blue     1            10
4    red   112           112
5   blue    10            10

answered Jan 10, 2022 at 20:39

wwnde

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