Pandas Groupby中两个系列的最大和最小 [英] Max and min from two series in pandas groupby

问题描述

是否可以从groupby中的两个系列中获得最小值和最大值?

Is it possible to get the min and max values from two series in a groupby?

例如，在以下情况下，按c分组时，如何同时获取a和b的最小值和最大值?

For example in the following situation, when grouping by c, how can I get the min and max values for a and b at the same time?

df = pd.DataFrame({'a': [10,20,3,40,55], 'b': [5,14,8,50,60], 'c': ['x','x','y','y','y']})
g = df.groupby(df.c)
for key, item in g:
    print (g.get_group(key), "\n")

    a   b  c
0  10   5  x
1  20  14  x

    a   b  c
2   3   8  y
3  40  50  y
4  55  60  y

我已经解决了这个问题，方法是取每个分组序列的最小值和最大值，然后找到_min/_max系列的最小值和最大值:

I have resolved this by taking the min and max of each grouped series then by finding the min and max of the _min/_max series:

df['a_min'] = g['a'].transform('min')
df['a_max'] = g['a'].transform('max')
df['b_min'] = g['b'].transform('min')
df['b_max'] = g['b'].transform('max')
df['min'] = df[['a_min', 'a_max', 'b_min', 'b_max']].min(axis=1)
df['max'] = df[['a_min', 'a_max', 'b_min', 'b_max']].max(axis=1)

    a   b  c  a_min  a_max  b_min  b_max  min  max
0  10   5  x     10     20      5     14    5   20
1  20  14  x     10     20      5     14    5   20
2   3   8  y      3     55      8     60    3   60
3  40  50  y      3     55      8     60    3   60
4  55  60  y      3     55      8     60    3   60

这产生了我想要的输出，但是有很多额外的系列.我想知道是否有更好的方法可以做到这一点?

This produces the output that I want but with a lot of extra series. I am wondering if there is a better way to do this?

推荐答案

使用transform仍然可以，您只需为transform结果添加min(axis=1)

Using transformstill ok , you just need add min(axis=1) for your transform result

df['min'],df['max']=df.groupby('c').transform('min').min(1),df.groupby('c').transform('max').max(1)
df
Out[88]: 
    a   b  c  min  max
0  10   5  x    5   20
1  20  14  x    5   20
2   3   8  y    3   60
3  40  50  y    3   60
4  55  60  y    3   60

在某些情况下，如果您不想包含某些系列，例如排除f，则应在分组之后列出该系列

In an instance where there are series that you don't want included, for example excluding f, the series should be listed after the grouping

    a   b  c   f
0  10   5  x   0
1  20  14  x  45
2   3   8  y  67
3  40  50  y  17
4  55  60  y  91

df['min'] = df.groupby('c')[['a', 'b']].transform('min').min(axis=1)
df['max'] = df.groupby('c')[['a', 'b']].transform('max').max(axis=1)

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