如何删除 pandas dataframe 中的重复项，但根据特定列值保留行

Question

I have a pandas dataframe with NBA player stats, and I want to drop the rows of duplicate players. There are duplicates because some players played on multiple teams for the 2020-2021 season, and I want to drop these duplicates. However, for these players that played on multiple teams, there is also a row with that player's combined stats across all teams and a team label of 'TOT', which represents the fact that that player played on 2 or more teams for the season. When I drop duplicate players, I want the row with the team of 'TOT' to remain, and all the other duplicates to be gone. I'm unsure of how to specify that I want to drop all duplicates, but keep the duplicate where df['Team'] = 'TOT'.

Here is what my dataframe looks like: Dataframe

In this example, I want to drop the duplicates of the player 'Jarrett Allen', but keep the row for Jarrett Allen where his team (Tm) is 'TOT'.

Answer 1

One way is to use a helper column. For example with the following df,

    player  stats team
0      bob      1  ABC
1    alice      2  DEF
2  charlie      3  GHI
3     mary      4  JKL
4     mary      5  MNO
5     mary      6  TOT
6      bob      7  TOT
7      bob      8  VWX

Creating a column where hte value is True if the 'team' value is 'TOT' and False otherwise results in:

import numpy as np

df['multiple_teams'] = np.where(df['team']=='TOT', 'TOT', None)

    player  stats team  multiple_teams
1    alice      2  DEF           False
0      bob      1  ABC           False
6      bob      7  TOT            True
7      bob      8  VWX           False
2  charlie      3  GHI           False
3     mary      4  JKL           False
4     mary      5  MNO           False
5     mary      6  TOT            True

Now we can use the keep parameter of the drop_duplicates() function to decide what to keep. In this case we can achieve the desired result by dropping the values based on the subset of player and multiple_teams with keep=False . This will mean that all duplicates across both columns will be removed from the df. Resulting in:

    player  stats team  multiple_teams
1    alice      2  DEF           False
6      bob      7  TOT            True
2  charlie      3  GHI           False
5     mary      6  TOT            True

Answer 2

You can just filter out unnecessary rows:

df = df.loc[(df['Rk'].duplicated(keep=False) == False) | (df['Tm'] == 'TOT'), :]

It can be understood this way: From my dataframe take all rows which are not duplicated in column 'Rk' or rows which have 'TOT' in column 'Tm'.

":" at the end means that you want to take all columns.

Answer 3

You can sort the DataFrame using the key argument, such that 'TOT' is sorted to the bottom and then drop_duplicates, keeping the last.

This guarantees that in the end there is only a single row per player, even if the data are messy and may have multiple 'TOT' rows for a single player, one team and one 'TOT' row, or multiple teams and multiple 'TOT' rows.

df = (df.sort_values('team', key=lambda x: x.eq('TOT'))
        .drop_duplicates('player', keep='last'))

---

print(df)
#    player  stats team
#0    alice      2  DEF
#1      bob      7  TOT
#2      bob      1  ABC
#3  charlie      3  GHI
#4     mary      4  JKL
#5     mary      5  MNO
#6     mary      6  TOT

df = (df.sort_values('team', key=lambda x: x.eq('TOT'))
        .drop_duplicates('player', keep='last'))

print(df)
#    player  stats team
#0    alice      2  DEF
#3  charlie      3  GHI
#1      bob      7  TOT
#6     mary      6  TOT