在multiindex数据框中查找列的最大值并返回其所有值

Question

数据集的可重现代码:

df = {'player' : ['a','a','a','a','a','a','a','a','a','b','b','b','b','b','b','b','b','b','c','c','c','c','c','c','c','c','c'],
      'week' : ['1','1','1','2','2','2','3','3','3','1','1','1','2','2','2','3','3','3','1','1','1','2','2','2','3','3','3'],
      'category': ['RES','VIT','MATCH','RES','VIT','MATCH','RES','VIT','MATCH','RES','VIT','MATCH','RES','VIT','MATCH','RES','VIT','MATCH','RES','VIT','MATCH','RES','VIT','MATCH','RES','VIT','MATCH'],
      'energy' : [75,54,87,65,24,82,65,42,35,25,45,87,98,54,82,75,54,87,65,24,82,65,42,35,25,45,98] }

df = pd.DataFrame(data= df)
df = df[['player', 'week', 'category','energy']]

我需要找到"对于每个玩家,找到他能量最大的那一周并显示所有类别,那个星期的能量值"

所以我做的是:

1.设置播放器和周作为索引

2.迭代索引以找到能量的最大值并返回其值

df = df.set_index(['player', 'week'])

for index, row in df1.iterrows():
    group = df1.ix[df1['energy'].idxmax()]

获得的产出:

                category energy
  player   week     
    b        2    RES      98
             2    VIT      54
             2   MATCH     82

这个获得的输出是针对整个数据集中的最大能量,我希望每个玩家拥有所有其他类别的最大值以及该周的能量.

预期产出:

我已尝试使用评论中建议的groupby方法,

df.groupby(['player','week'])['energy'].max().groupby(level=['player','week'])

获得的输出是:

                energy  category
 player week        
   a     1        87    VIT
         2        82    VIT
         3        65    VIT
   b     1        87    VIT
         2        98    VIT
         3        87    VIT
   c     1        82    VIT
         2        65    VIT
         3        98    VIT

Answer 1

找到每个玩家的最大能量周，然后为该玩家选择该周并将所有玩家的结果连接起来。

max_energy_idx = df.groupby('player')['energy'].idxmax()  # 2, 12, 26
max_energy_weeks = df['week'].iloc[max_energy_idx]  # '1', '2', '3'
players = sorted(df['player'].unique())  # 'a', 'b', 'c'

result = pd.concat(
    [df.loc[(df['player'] == player) & (df['week'] == max_enery_week), :] 
     for player, max_enery_week in zip(players, max_energy_weeks)]
)
>>> result
   player week category  energy
0       a    1      RES      75
1       a    1      VIT      54
2       a    1    MATCH      87
12      b    2      RES      98
13      b    2      VIT      54
14      b    2    MATCH      82
24      c    3      RES      25
25      c    3      VIT      45
26      c    3    MATCH      98

如果需要，您可以在结果上设置索引：

result = result.set_index(['player', 'week'])