如何根据 pandas 中的列值对数据进行分类？

Question

假设我有这个数据框：

raw_data = {'regiment': ['Nighthawks', 'Nighthawks', 'Nighthawks', 'Nighthawks', 'Dragoons', 'Dragoons', 'Dragoons', 'Dragoons', 'Scouts', 'Scouts', 'Scouts', 'Scouts'], 
        'payout': [.1, .15, .2, .3, 1.2, 1.3, 1.45, 2, 2.04, 3.011, 3.45, 1], 
        'name': ['Miller', 'Jacobson', 'Ali', 'Milner', 'Cooze', 'Jacon', 'Ryaner', 'Sone', 'Sloan', 'Piger', 'Riani', 'Ali'], 
        'preTestScore': [4, 24, 31, 2, 3, 4, 24, 31, 2, 3, 2, 3],
        'postTestScore': [25, 94, 57, 62, 70, 25, 94, 57, 62, 70, 62, 70]}
df = pd.DataFrame(raw_data, columns = ['regiment', 'payout', 'name', 'preTestScore', 'postTestScore'])

现在，我想根据 "payout" 列构建这些类别：

Cat1 : 0 <= x <= 1
Cat2 : 1 <  x <= 2
Cat3 : 2 <  x <= 3
Cat4 : 3 <  x <= 4

并构建 postTestscore

列的总和

我是这样做的，使用布尔索引：

df.loc[(df['payout'] > 0) & (df['payout'] <= 1), 'postTestScore'].sum()
df.loc[(df['payout'] > 1) & (df['payout'] <= 2), 'postTestScore'].sum()
etc...

很好用，但是有人知道这个更简洁（pythonic）的解决方案吗？

Answer 1

尝试 pd.cut 和 groupby:

df.groupby(pd.cut(df.payout, [0, 1, 2, 3, 4])).postTestScore.sum()

payout
(0, 1]    308
(1, 2]    246
(2, 3]     62
(3, 4]    132
Name: postTestScore, dtype: int64

Answer 2

按 cut 创建类别，然后 groupby 总和：

bins = [0,1,2,3,4]
labels=['Cat{}'.format(x) for x in range(1, len(bins))]
binned = pd.cut(df['payout'], bins=bins, labels=labels)
print (binned)
0     Cat1
1     Cat1
2     Cat1
3     Cat1
4     Cat2
5     Cat2
6     Cat2
7     Cat2
8     Cat3
9     Cat4
10    Cat4
11    Cat1
Name: payout, dtype: category
Categories (4, object): [Cat1 < Cat2 < Cat3 < Cat4]

df1 = df.groupby(binned)['postTestScore'].sum().reset_index()
print (df1)
  payout  postTestScore
0   Cat1            308
1   Cat2            246
2   Cat3             62
3   Cat4            132

同样是一行解法：

df1 = df.groupby(pd.cut(df['payout'], 
                        bins=[0,1,2,3,4], 
                        labels=['Cat1','Cat2','Cat3','Cat4']))['postTestScore'].sum()
print (df1)

payout
Cat1    308
Cat2    246
Cat3     62
Cat4    132
Name: postTestScore, dtype: int64

numpy 的另一个非常快速的解决方案：

labs = ['Cat{}'.format(x) for x in range(len(bins))]
a = np.array(labs)[np.array(bins).searchsorted(df['payout'].values)]
print (a)

['Cat1' 'Cat1' 'Cat1' 'Cat1' 'Cat2' 'Cat2' 'Cat2' 'Cat2' 'Cat3' 'Cat4'
 'Cat4' 'Cat1']

df1 = df.groupby(a)['postTestScore'].sum().rename_axis('cats').reset_index()
print (df1)
   cats  postTestScore
0  Cat1            308
1  Cat2            246
2  Cat3             62
3  Cat4            132

如何根据 pandas 中的列值对数据进行分类？

How to categorize data based on column values in pandas?

python

categories

dataframe

pandas