索引
Series的索引(obj[…])与Numpy数组索引的功能类似,只不过Series的索引值可以不是整数。
import numpy as np
import pandas as pd
obj=pd.Series(np.arange(4.),index=['a','b','c','d'])
obj
普通的python切片不包含尾部
a 0.0
b 1.0
c 2.0
d 3.0
dtype: float64
使用这些方法会修改Series的相应部分:
obj['b':'c']=5
obj
a 0.0
b 5.0
c 5.0
d 3.0
dtype: float64
import numpy as np
import pandas as pd
df = pd.read_csv('data/table.csv',index_col='ID')
df.head()
|
School |
Class |
Gender |
Address |
Height |
Weight |
Math |
Physics |
ID |
|
|
|
|
|
|
|
|
1101 |
S_1 |
C_1 |
M |
street_1 |
173 |
63 |
34.0 |
A+ |
1102 |
S_1 |
C_1 |
F |
street_2 |
192 |
73 |
32.5 |
B+ |
1103 |
S_1 |
C_1 |
M |
street_2 |
186 |
82 |
87.2 |
B+ |
1104 |
S_1 |
C_1 |
F |
street_2 |
167 |
81 |
80.4 |
B- |
1105 |
S_1 |
C_1 |
F |
street_4 |
159 |
64 |
84.8 |
B+ |
使用单个值或者序列,可以从DataFrame中索引出一个或多个列
df['School']
df[['School','Class']]
这种索引也有特殊案例。首先可以根据一个布尔数组切片或者选择数据:
df[:2]
|
School |
Class |
Gender |
Address |
Height |
Weight |
Math |
Physics |
ID |
|
|
|
|
|
|
|
|
1101 |
S_1 |
C_1 |
M |
street_1 |
173 |
63 |
34.0 |
A+ |
1102 |
S_1 |
C_1 |
F |
street_2 |
192 |
73 |
32.5 |
B+ |
df[df['Physics']=='A+']
|
School |
Class |
Gender |
Address |
Height |
Weight |
Math |
Physics |
ID |
|
|
|
|
|
|
|
|
1101 |
S_1 |
C_1 |
M |
street_1 |
173 |
63 |
34.0 |
A+ |
1203 |
S_1 |
C_2 |
M |
street_6 |
160 |
53 |
58.8 |
A+ |
2203 |
S_2 |
C_2 |
M |
street_4 |
155 |
91 |
73.8 |
A+ |
使用布尔值DataFrame进行索引,布尔值DataFrame可以是对表两只进行比较产生的。
这种索引方式在语法上更像是Numpy二维数组。
1.单级索引
1. 1 loc方法、iloc方法、[ ]操作符
最常用的索引方法可能就是这三类,其中iloc表示位置索引,loc表示标签索引,[ ]也具有很大的便利性,各有特点
1.1.1 loc方法(注意:所有在loc中使用的切片全部包含右端点!)
① 单行索引:
df.loc[1103]
School S_1
Class C_1
Gender M
Address street_2
Height 186
Weight 82
Math 87.2
Physics B+
Name: 1103, dtype: object
② 多行索引:
df.loc[[1102,2304]]
|
School |
Class |
Gender |
Address |
Height |
Weight |
Math |
Physics |
ID |
|
|
|
|
|
|
|
|
1102 |
S_1 |
C_1 |
F |
street_2 |
192 |
73 |
32.5 |
B+ |
2304 |
S_2 |
C_3 |
F |
street_6 |
164 |
81 |
95.5 |
A- |
df.loc[1304:].head()
|
School |
Class |
Gender |
Address |
Height |
Weight |
Math |
Physics |
ID |
|
|
|
|
|
|
|
|
1304 |
S_1 |
C_3 |
M |
street_2 |
195 |
70 |
85.2 |
A |
1305 |
S_1 |
C_3 |
F |
street_5 |
187 |
69 |
61.7 |
B- |
2101 |
S_2 |
C_1 |
M |
street_7 |
174 |
84 |
83.3 |
C |
2102 |
S_2 |
C_1 |
F |
street_6 |
161 |
61 |
50.6 |
B+ |
2103 |
S_2 |
C_1 |
M |
street_4 |
157 |
61 |
52.5 |
B- |
df.loc[2402::-1].head()
|
School |
Class |
Gender |
Address |
Height |
Weight |
Math |
Physics |
ID |
|
|
|
|
|
|
|
|
2402 |
S_2 |
C_4 |
M |
street_7 |
166 |
82 |
48.7 |
B |
2401 |
S_2 |
C_4 |
F |
street_2 |
192 |
62 |
45.3 |
A |
2305 |
S_2 |
C_3 |
M |
street_4 |
187 |
73 |
48.9 |
B |
2304 |
S_2 |
C_3 |
F |
street_6 |
164 |
81 |
95.5 |
A- |
2303 |
S_2 |
C_3 |
F |
street_7 |
190 |
99 |
65.9 |
C |
③ 单列索引:
df.loc[:,'Height'].head()
ID
1101 173
1102 192
1103 186
1104 167
1105 159
Name: Height, dtype: int64
④ 多列索引:
df.loc[:,['Height','Math']].head()
|
Height |
Math |
ID |
|
|
1101 |
173 |
34.0 |
1102 |
192 |
32.5 |
1103 |
186 |
87.2 |
1104 |
167 |
80.4 |
1105 |
159 |
84.8 |
df.loc[:,'Height':'Math'].head()
|
Height |
Weight |
Math |
ID |
|
|
|
1101 |
173 |
63 |
34.0 |
1102 |
192 |
73 |
32.5 |
1103 |
186 |
82 |
87.2 |
1104 |
167 |
81 |
80.4 |
1105 |
159 |
64 |
84.8 |
⑥ 函数式索引:
df.loc[lambda x:x['Gender']=='M'].head()
|
School |
Class |
Gender |
Address |
Height |
Weight |
Math |
Physics |
ID |
|
|
|
|
|
|
|
|
1101 |
S_1 |
C_1 |
M |
street_1 |
173 |
63 |
34.0 |
A+ |
1103 |
S_1 |
C_1 |
M |
street_2 |
186 |
82 |
87.2 |
B+ |
1201 |
S_1 |
C_2 |
M |
street_5 |
188 |
68 |
97.0 |
A- |
1203 |
S_1 |
C_2 |
M |
street_6 |
160 |
53 |
58.8 |
A+ |
1301 |
S_1 |
C_3 |
M |
street_4 |
161 |
68 |
31.5 |
B+ |
def f(x):
return [1101,1103]
df.loc[f]
|
School |
Class |
Gender |
Address |
Height |
Weight |
Math |
Physics |
ID |
|
|
|
|
|
|
|
|
1101 |
S_1 |
C_1 |
M |
street_1 |
173 |
63 |
34.0 |
A+ |
1103 |
S_1 |
C_1 |
M |
street_2 |
186 |
82 |
87.2 |
B+ |
⑦ 布尔索引
df.loc[df['Address'].isin(['street_7','street_4'])].head()
|
School |
Class |
Gender |
Address |
Height |
Weight |
Math |
Physics |
ID |
|
|
|
|
|
|
|
|
1105 |
S_1 |
C_1 |
F |
street_4 |
159 |
64 |
84.8 |
B+ |
1202 |
S_1 |
C_2 |
F |
street_4 |
176 |
94 |
63.5 |
B- |
1301 |
S_1 |
C_3 |
M |
street_4 |
161 |
68 |
31.5 |
B+ |
1303 |
S_1 |
C_3 |
M |
street_7 |
188 |
82 |
49.7 |
B |
2101 |
S_2 |
C_1 |
M |
street_7 |
174 |
84 |
83.3 |
C |
df.loc[[True if i[-1]=='4' or i[-1]=='7' else False for i in df['Address'].values]].head()
|
School |
Class |
Gender |
Address |
Height |
Weight |
Math |
Physics |
ID |
|
|
|
|
|
|
|
|
1105 |
S_1 |
C_1 |
F |
street_4 |
159 |
64 |
84.8 |
B+ |
1202 |
S_1 |
C_2 |
F |
street_4 |
176 |
94 |
63.5 |
B- |
1301 |
S_1 |
C_3 |
M |
street_4 |
161 |
68 |
31.5 |
B+ |
1303 |
S_1 |
C_3 |
M |
street_7 |
188 |
82 |
49.7 |
B |
2101 |
S_2 |
C_1 |
M |
street_7 |
174 |
84 |
83.3 |
C |
当然也有相对简便的写法:
df[df['Address'].str.contains('4|7')].head()
本质上说,loc中能传入的只有布尔列表和索引子集构成的列表,只要把握这个原则就很容易理解上面那些操作
1.1.2 iloc方法(注意与loc不同,切片右端点不包含)
- 单行索引:
df.iloc[3]
School S_1
Class C_1
Gender F
Address street_2
Height 167
Weight 81
Math 80.4
Physics B-
Name: 1104, dtype: object
- 多行索引:
df.iloc[3:5]
|
School |
Class |
Gender |
Address |
Height |
Weight |
Math |
Physics |
ID |
|
|
|
|
|
|
|
|
1104 |
S_1 |
C_1 |
F |
street_2 |
167 |
81 |
80.4 |
B- |
1105 |
S_1 |
C_1 |
F |
street_4 |
159 |
64 |
84.8 |
B+ |
3.单列索引:
df.iloc[:,3].head()
ID
1101 street_1
1102 street_2
1103 street_2
1104 street_2
1105 street_4
Name: Address, dtype: object
- 多列索引:
df.iloc[:,7::-2].head()
|
Physics |
Weight |
Address |
Class |
ID |
|
|
|
|
1101 |
A+ |
63 |
street_1 |
C_1 |
1102 |
B+ |
73 |
street_2 |
C_1 |
1103 |
B+ |
82 |
street_2 |
C_1 |
1104 |
B- |
81 |
street_2 |
C_1 |
1105 |
B+ |
64 |
street_4 |
C_1 |
- 混合索引:
df.iloc[3::4,7::-2].head()
|
Physics |
Weight |
Address |
Class |
ID |
|
|
|
|
1104 |
B- |
81 |
street_2 |
C_1 |
1203 |
A+ |
53 |
street_6 |
C_2 |
1302 |
A- |
57 |
street_1 |
C_3 |
2101 |
C |
84 |
street_7 |
C_1 |
2105 |
A |
81 |
street_4 |
C_1 |
- 函数式索引:
df.iloc[lambda x:[3]].head()
|
School |
Class |
Gender |
Address |
Height |
Weight |
Math |
Physics |
ID |
|
|
|
|
|
|
|
|
1104 |
S_1 |
C_1 |
F |
street_2 |
167 |
81 |
80.4 |
B- |
由上所述,iloc中接收的参数只能为整数或整数列表,不能使用布尔索引
(c) [ ]操作符
如果不想陷入困境,请不要在行索引为浮点时使用 [ ]操作符,因为在Series中的浮点 [ ]并不是进行位置比较,而是值比较,非常特殊
- Series的 [ ]操作
1.1 单元素索引:
s = pd.Series(df['Math'],index=df.index)
s[1101]
34.0
1.2 多行索引:
s[0:4]
ID
1101 34.0
1102 32.5
1103 87.2
1104 80.4
Name: Math, dtype: float64
1.3 函数式索引:
s[lambda x: x.index[16::-6]]
ID
2102 50.6
1301 31.5
1105 84.8
Name: Math, dtype: float64
1.4 布尔索引:
s[s>80]
ID
1103 87.2
1104 80.4
1105 84.8
1201 97.0
1302 87.7
1304 85.2
2101 83.3
2205 85.4
2304 95.5
Name: Math, dtype: float64
- DataFrame的[ ]操作
2.1 单行索引:
df[1:2]
|
School |
Class |
Gender |
Address |
Height |
Weight |
Math |
Physics |
ID |
|
|
|
|
|
|
|
|
1102 |
S_1 |
C_1 |
F |
street_2 |
192 |
73 |
32.5 |
B+ |
row = df.index.get_loc(1102)
df[row:row+1]
|
School |
Class |
Gender |
Address |
Height |
Weight |
Math |
Physics |
ID |
|
|
|
|
|
|
|
|
1102 |
S_1 |
C_1 |
F |
street_2 |
192 |
73 |
32.5 |
B+ |
2.2 多行索引:
df[3:5]
|
School |
Class |
Gender |
Address |
Height |
Weight |
Math |
Physics |
ID |
|
|
|
|
|
|
|
|
1104 |
S_1 |
C_1 |
F |
street_2 |
167 |
81 |
80.4 |
B- |
1105 |
S_1 |
C_1 |
F |
street_4 |
159 |
64 |
84.8 |
B+ |
2.3 单列索引:
df['School'].head()
ID
1101 S_1
1102 S_1
1103 S_1
1104 S_1
1105 S_1
Name: School, dtype: object
2.4 多列索引:
df[['School','Math']].head()
|
School |
Math |
ID |
|
|
1101 |
S_1 |
34.0 |
1102 |
S_1 |
32.5 |
1103 |
S_1 |
87.2 |
1104 |
S_1 |
80.4 |
1105 |
S_1 |
84.8 |
2.5 函数式索引:
df[lambda x:['Math','Physics']].head()
|
Math |
Physics |
ID |
|
|
1101 |
34.0 |
A+ |
1102 |
32.5 |
B+ |
1103 |
87.2 |
B+ |
1104 |
80.4 |
B- |
1105 |
84.8 |
B+ |
2.6 布尔索引:
df[df['Gender']=='F'].head()
|
School |
Class |
Gender |
Address |
Height |
Weight |
Math |
Physics |
ID |
|
|
|
|
|
|
|
|
1102 |
S_1 |
C_1 |
F |
street_2 |
192 |
73 |
32.5 |
B+ |
1104 |
S_1 |
C_1 |
F |
street_2 |
167 |
81 |
80.4 |
B- |
1105 |
S_1 |
C_1 |
F |
street_4 |
159 |
64 |
84.8 |
B+ |
1202 |
S_1 |
C_2 |
F |
street_4 |
176 |
94 |
63.5 |
B- |
1204 |
S_1 |
C_2 |
F |
street_5 |
162 |
63 |
33.8 |
B |
一般来说,[]操作符常用于列选择或布尔选择,尽量避免行的选择.
1.2 布尔索引
1.2.1 布尔符号:’&’,’|’,’~’:分别代表和and,或or,取反not
df[(df['Gender']=='F')&(df['Address']=='street_2')].head()
|
School |
Class |
Gender |
Address |
Height |
Weight |
Math |
Physics |
ID |
|
|
|
|
|
|
|
|
1102 |
S_1 |
C_1 |
F |
street_2 |
192 |
73 |
32.5 |
B+ |
1104 |
S_1 |
C_1 |
F |
street_2 |
167 |
81 |
80.4 |
B- |
2401 |
S_2 |
C_4 |
F |
street_2 |
192 |
62 |
45.3 |
A |
2404 |
S_2 |
C_4 |
F |
street_2 |
160 |
84 |
67.7 |
B |
df[(df['Math']>85)|(df['Address']=='street_7')].head()
|
School |
Class |
Gender |
Address |
Height |
Weight |
Math |
Physics |
ID |
|
|
|
|
|
|
|
|
1103 |
S_1 |
C_1 |
M |
street_2 |
186 |
82 |
87.2 |
B+ |
1201 |
S_1 |
C_2 |
M |
street_5 |
188 |
68 |
97.0 |
A- |
1302 |
S_1 |
C_3 |
F |
street_1 |
175 |
57 |
87.7 |
A- |
1303 |
S_1 |
C_3 |
M |
street_7 |
188 |
82 |
49.7 |
B |
1304 |
S_1 |
C_3 |
M |
street_2 |
195 |
70 |
85.2 |
A |
df[~((df['Math']>75)|(df['Address']=='street_1'))].head()
|
School |
Class |
Gender |
Address |
Height |
Weight |
Math |
Physics |
ID |
|
|
|
|
|
|
|
|
1102 |
S_1 |
C_1 |
F |
street_2 |
192 |
73 |
32.5 |
B+ |
1202 |
S_1 |
C_2 |
F |
street_4 |
176 |
94 |
63.5 |
B- |
1203 |
S_1 |
C_2 |
M |
street_6 |
160 |
53 |
58.8 |
A+ |
1204 |
S_1 |
C_2 |
F |
street_5 |
162 |
63 |
33.8 |
B |
1205 |
S_1 |
C_2 |
F |
street_6 |
167 |
63 |
68.4 |
B- |
loc和[]中相应位置都能使用布尔列表选择:
df.loc[df['Math']>60,(df[:8]['Address']=='street_6').values].head()
|
Physics |
ID |
|
1103 |
B+ |
1104 |
B- |
1105 |
B+ |
1201 |
A- |
1202 |
B- |
1.2.2 isin方法
df[df['Address'].isin(['street_1','street_4'])&df['Physics'].isin(['A','A+'])]
|
School |
Class |
Gender |
Address |
Height |
Weight |
Math |
Physics |
ID |
|
|
|
|
|
|
|
|
1101 |
S_1 |
C_1 |
M |
street_1 |
173 |
63 |
34.0 |
A+ |
2105 |
S_2 |
C_1 |
M |
street_4 |
170 |
81 |
34.2 |
A |
2203 |
S_2 |
C_2 |
M |
street_4 |
155 |
91 |
73.8 |
A+ |
df[df[['Address','Physics']].isin({'Address':['street_1','street_4'],'Physics':['A','A+']}).all(1)]
|
School |
Class |
Gender |
Address |
Height |
Weight |
Math |
Physics |
ID |
|
|
|
|
|
|
|
|
1101 |
S_1 |
C_1 |
M |
street_1 |
173 |
63 |
34.0 |
A+ |
2105 |
S_2 |
C_1 |
M |
street_4 |
170 |
81 |
34.2 |
A |
2203 |
S_2 |
C_2 |
M |
street_4 |
155 |
91 |
73.8 |
A+ |
1.2.3 快速标量索引
当只需要取一个元素时,at和iat方法能够提供更快的实现:
display(df.at[1101,'School'])
display(df.loc[1101,'School'])
display(df.iat[0,0])
display(df.iloc[0,0])
'S_1'
'S_1'
'S_1'
'S_1'
1.2.4 区间索引
1.2.4.1利用interval_range方法
pd.interval_range(start=0,end=5)
IntervalIndex([(0, 1], (1, 2], (2, 3], (3, 4], (4, 5]],
closed='right',
dtype='interval[int64]')
pd.interval_range(start=0,periods=8,freq=5)
IntervalIndex([(0, 5], (5, 10], (10, 15], (15, 20], (20, 25], (25, 30], (30, 35], (35, 40]],
closed='right',
dtype='interval[int64]')
1.2.4.2 利用cut将数值列转为区间为元素的分类变量
例如统计数学成绩的区间情况:
math_interval = pd.cut(df['Math'],bins=[0,40,60,80,100])
math_interval.head()
ID
1101 (0, 40]
1102 (0, 40]
1103 (80, 100]
1104 (80, 100]
1105 (80, 100]
Name: Math, dtype: category
Categories (4, interval[int64]): [(0, 40] < (40, 60] < (60, 80] < (80, 100]]
1.2.5 区间索引的选取
df_i = df.join(math_interval,rsuffix='_interval')[['Math','Math_interval']]\
.reset_index().set_index('Math_interval')
df_i.head()
|
ID |
Math |
Math_interval |
|
|
(0, 40] |
1101 |
34.0 |
(0, 40] |
1102 |
32.5 |
(80, 100] |
1103 |
87.2 |
(80, 100] |
1104 |
80.4 |
(80, 100] |
1105 |
84.8 |
df_i.loc[65].head()
|
ID |
Math |
Math_interval |
|
|
(60, 80] |
1202 |
63.5 |
(60, 80] |
1205 |
68.4 |
(60, 80] |
1305 |
61.7 |
(60, 80] |
2104 |
72.2 |
(60, 80] |
2202 |
68.5 |
df_i.loc[[65,90]].head()
|
ID |
Math |
Math_interval |
|
|
(60, 80] |
1202 |
63.5 |
(60, 80] |
1205 |
68.4 |
(60, 80] |
1305 |
61.7 |
(60, 80] |
2104 |
72.2 |
(60, 80] |
2202 |
68.5 |
如果想要选取某个区间,先要把分类变量转为区间变量,再使用overlap方法:
df_i[df_i.index.astype('interval').overlaps(pd.Interval(70, 85))].head()
|
ID |
Math |
Math_interval |
|
|
(80, 100] |
1103 |
87.2 |
(80, 100] |
1104 |
80.4 |
(80, 100] |
1105 |
84.8 |
(80, 100] |
1201 |
97.0 |
(60, 80] |
1202 |
63.5 |
2 多级索引
2.1 创建多级索引
2.1.1 通过from_tuple或from_arrays
- 直接创建元组
tuples = [('A','a'),('A','b'),('B','a'),('B','b')]
mul_index = pd.MultiIndex.from_tuples(tuples, names=('Upper', 'Lower'))
mul_index
MultiIndex([('A', 'a'),
('A', 'b'),
('B', 'a'),
('B', 'b')],
names=['Upper', 'Lower'])
pd.DataFrame({'Score':['perfect','good','fair','bad']},index=mul_index)
|
|
Score |
Upper |
Lower |
|
A |
a |
perfect |
|
b |
good |
B |
a |
fair |
|
b |
bad |
- 利用zip创建元组:
L1 = list('AABB')
L2 = list('abab')
tuples = list(zip(L1,L2))
mul_index = pd.MultiIndex.from_tuples(tuples, names=('Upper', 'Lower'))
pd.DataFrame({'Score':['perfect','good','fair','bad']},index=mul_index)
|
|
Score |
Upper |
Lower |
|
A |
a |
perfect |
|
b |
good |
B |
a |
fair |
|
b |
bad |
- 通过Array创建
arrays = [['A','a'],['A','b'],['B','a'],['B','b']]
mul_index = pd.MultiIndex.from_tuples(arrays, names=('Upper', 'Lower'))
pd.DataFrame({'Score':['perfect','good','fair','bad']},index=mul_index)
|
|
Score |
Upper |
Lower |
|
A |
a |
perfect |
|
b |
good |
B |
a |
fair |
|
b |
bad |
mul_index
MultiIndex([('A', 'a'),
('A', 'b'),
('B', 'a'),
('B', 'b')],
names=['Upper', 'Lower'])
2.1.2 通过from_product
L1 = ['A','B']
L2 = ['a','b']
pd.MultiIndex.from_product([L1,L2],names=('Upper', 'Lower'))
MultiIndex([('A', 'a'),
('A', 'b'),
('B', 'a'),
('B', 'b')],
names=['Upper', 'Lower'])
2.1.3 指定df中的列创建(set_index方法)
df_using_mul = df.set_index(['Class','Address'])
df_using_mul.head()
|
|
School |
Gender |
Height |
Weight |
Math |
Physics |
Class |
Address |
|
|
|
|
|
|
C_1 |
street_1 |
S_1 |
M |
173 |
63 |
34.0 |
A+ |
|
street_2 |
S_1 |
F |
192 |
73 |
32.5 |
B+ |
|
street_2 |
S_1 |
M |
186 |
82 |
87.2 |
B+ |
|
street_2 |
S_1 |
F |
167 |
81 |
80.4 |
B- |
|
street_4 |
S_1 |
F |
159 |
64 |
84.8 |
B+ |
2.2 多层索引切片
df_using_mul.head()
|
|
School |
Gender |
Height |
Weight |
Math |
Physics |
Class |
Address |
|
|
|
|
|
|
C_1 |
street_1 |
S_1 |
M |
173 |
63 |
34.0 |
A+ |
|
street_2 |
S_1 |
F |
192 |
73 |
32.5 |
B+ |
|
street_2 |
S_1 |
M |
186 |
82 |
87.2 |
B+ |
|
street_2 |
S_1 |
F |
167 |
81 |
80.4 |
B- |
|
street_4 |
S_1 |
F |
159 |
64 |
84.8 |
B+ |
2.2.1 一般切片
df_using_mul.sort_index().loc['C_2','street_5']
|
|
School |
Gender |
Height |
Weight |
Math |
Physics |
Class |
Address |
|
|
|
|
|
|
C_2 |
street_5 |
S_1 |
M |
188 |
68 |
97.0 |
A- |
|
street_5 |
S_1 |
F |
162 |
63 |
33.8 |
B |
|
street_5 |
S_2 |
M |
193 |
100 |
39.1 |
B |
df_using_mul.sort_index().loc[('C_2','street_6'):('C_3','street_4')]
|
|
School |
Gender |
Height |
Weight |
Math |
Physics |
Class |
Address |
|
|
|
|
|
|
C_2 |
street_6 |
S_1 |
M |
160 |
53 |
58.8 |
A+ |
|
street_6 |
S_1 |
F |
167 |
63 |
68.4 |
B- |
|
street_7 |
S_2 |
F |
194 |
77 |
68.5 |
B+ |
|
street_7 |
S_2 |
F |
183 |
76 |
85.4 |
B |
C_3 |
street_1 |
S_1 |
F |
175 |
57 |
87.7 |
A- |
|
street_2 |
S_1 |
M |
195 |
70 |
85.2 |
A |
|
street_4 |
S_1 |
M |
161 |
68 |
31.5 |
B+ |
|
street_4 |
S_2 |
F |
157 |
78 |
72.3 |
B+ |
|
street_4 |
S_2 |
M |
187 |
73 |
48.9 |
B |
df_using_mul.sort_index().loc[('C_2','street_7'):'C_3'].head()
|
|
School |
Gender |
Height |
Weight |
Math |
Physics |
Class |
Address |
|
|
|
|
|
|
C_2 |
street_7 |
S_2 |
F |
194 |
77 |
68.5 |
B+ |
|
street_7 |
S_2 |
F |
183 |
76 |
85.4 |
B |
C_3 |
street_1 |
S_1 |
F |
175 |
57 |
87.7 |
A- |
|
street_2 |
S_1 |
M |
195 |
70 |
85.2 |
A |
|
street_4 |
S_1 |
M |
161 |
68 |
31.5 |
B+ |
2.2.2 第一类特殊情况:由元组构成列表
df_using_mul.sort_index().loc[[('C_2','street_7'),('C_3','street_2')]]
|
|
School |
Gender |
Height |
Weight |
Math |
Physics |
Class |
Address |
|
|
|
|
|
|
C_2 |
street_7 |
S_2 |
F |
194 |
77 |
68.5 |
B+ |
|
street_7 |
S_2 |
F |
183 |
76 |
85.4 |
B |
C_3 |
street_2 |
S_1 |
M |
195 |
70 |
85.2 |
A |
2.2.3 第二类特殊情况:由列表构成元组
df_using_mul.sort_index().loc[(['C_2','C_3'],['street_4','street_7']),:]
|
|
School |
Gender |
Height |
Weight |
Math |
Physics |
Class |
Address |
|
|
|
|
|
|
C_2 |
street_4 |
S_1 |
F |
176 |
94 |
63.5 |
B- |
|
street_4 |
S_2 |
M |
155 |
91 |
73.8 |
A+ |
|
street_7 |
S_2 |
F |
194 |
77 |
68.5 |
B+ |
|
street_7 |
S_2 |
F |
183 |
76 |
85.4 |
B |
C_3 |
street_4 |
S_1 |
M |
161 |
68 |
31.5 |
B+ |
|
street_4 |
S_2 |
F |
157 |
78 |
72.3 |
B+ |
|
street_4 |
S_2 |
M |
187 |
73 |
48.9 |
B |
|
street_7 |
S_1 |
M |
188 |
82 |
49.7 |
B |
|
street_7 |
S_2 |
F |
190 |
99 |
65.9 |
C |
2.3 多层索引中的slice对象
L1,L2 = ['A','B','C'],['a','b','c']
mul_index1 = pd.MultiIndex.from_product([L1,L2],names=('Upper', 'Lower'))
L3,L4 = ['D','E','F'],['d','e','f']
mul_index2 = pd.MultiIndex.from_product([L3,L4],names=('Big', 'Small'))
df_s = pd.DataFrame(np.random.rand(9,9),index=mul_index1,columns=mul_index2)
df_s
Big |
|
|
|
D |
|
|
E |
|
|
F |
|
Small |
|
d |
e |
f |
d |
e |
f |
d |
e |
f |
|
Upper |
Lower |
|
|
|
|
|
|
|
|
|
|
A |
a |
0.294849 |
0.808944 |
0.286861 |
0.079801 |
0.498002 |
0.974476 |
0.261653 |
0.792329 |
0.671085 |
|
|
b |
0.038281 |
0.802229 |
0.689221 |
0.258438 |
0.526583 |
0.527028 |
0.662287 |
0.424268 |
0.312776 |
|
|
c |
0.360262 |
0.096973 |
0.491884 |
0.843597 |
0.040154 |
0.563663 |
0.065939 |
0.342367 |
0.928119 |
|
B |
a |
0.483322 |
0.226118 |
0.695874 |
0.804036 |
0.056607 |
0.405535 |
0.960890 |
0.409557 |
0.044850 |
|
|
b |
0.902773 |
0.889656 |
0.212978 |
0.986362 |
0.733843 |
0.234746 |
0.266932 |
0.360693 |
0.856747 |
|
|
c |
0.204079 |
0.424308 |
0.878692 |
0.027883 |
0.604838 |
0.292223 |
0.814461 |
0.633649 |
0.195861 |
|
C |
a |
0.745168 |
0.065248 |
0.408881 |
0.647361 |
0.042335 |
0.245639 |
0.351357 |
0.945664 |
0.546389 |
|
|
b |
0.682388 |
0.948741 |
0.072672 |
0.179705 |
0.775370 |
0.565560 |
0.935742 |
0.149620 |
0.806942 |
|
|
c |
0.079893 |
0.031765 |
0.425390 |
0.557884 |
0.827765 |
0.650221 |
0.519717 |
0.708033 |
0.128069 |
|
idx=pd.IndexSlice
df_s.loc[idx['B':,df_s['D']['d']>0.3],idx[df_s.sum()>4]]
Big |
D |
E |
F |
|
|
|
|
Small |
|
d |
e |
f |
e |
f |
e |
Upper |
Lower |
|
|
|
|
|
|
B |
a |
0.8898 |
0.364698 |
0.347762 |
0.975053 |
0.494357 |
0.600218 |
|
b |
0.831198 |
0.922369 |
0.121323 |
0.104072 |
0.965247 |
0.951544 |
C |
a |
0.469555 |
0.202389 |
0.360323 |
0.789773 |
0.620175 |
0.284863 |
|
c |
0.684378 |
0.494056 |
0.995441 |
0.738033 |
0.198539 |
0.770315 |
2.4 索引层的交换
2.4.1 swaplevel方法(两层交换)
df_using_mul.head()
Class |
Address |
|
|
|
|
|
|
C_1 |
street_1 |
S_1 |
M |
173 |
63 |
34 |
A+ |
|
street_2 |
S_1 |
F |
192 |
73 |
32.5 |
B+ |
|
street_2 |
S_1 |
M |
186 |
82 |
87.2 |
B+ |
|
street_2 |
S_1 |
F |
167 |
81 |
80.4 |
B- |
|
street_4 |
S_1 |
F |
159 |
64 |
84.8 |
B+ |
df_using_mul.swaplevel(i=1,j=0,axis=0).sort_index().head()
|
School |
Gender |
Height |
Weight |
Math |
Physics |
|
Address |
Class |
|
|
|
|
|
|
street_1 |
C_1 |
S_1 |
M |
173 |
63 |
34 |
A+ |
|
C_2 |
S_2 |
M |
175 |
74 |
47.2 |
B- |
|
C_3 |
S_1 |
F |
175 |
57 |
87.7 |
A- |
street_2 |
C_1 |
S_1 |
F |
192 |
73 |
32.5 |
B+ |
|
C_1 |
S_1 |
M |
186 |
82 |
87.2 |
B+ |
2.4.2 reorder_levels方法(多层交换)
df_muls = df.set_index(['School','Class','Address'])
df_muls.head()
|
Gender |
Height |
Weight |
Math |
Physics |
|
|
School |
Class |
Address |
|
|
|
|
|
S_1 |
C_1 |
street_1 |
M |
173 |
63 |
34 |
A+ |
|
|
street_2 |
F |
192 |
73 |
32.5 |
B+ |
|
|
street_2 |
M |
186 |
82 |
87.2 |
B+ |
|
|
street_2 |
F |
167 |
81 |
80.4 |
B- |
|
|
street_4 |
F |
159 |
64 |
84.8 |
B+ |
df_muls.reorder_levels([2,0,1],axis=0).sort_index().head()
|
|
|
Gender |
Height |
Weight |
Math |
Physics |
Address |
School |
Class |
|
|
|
|
|
street_1 |
S_1 |
C_1 |
M |
173 |
63 |
34 |
A+ |
|
|
C_3 |
F |
175 |
57 |
87.7 |
A- |
|
S_2 |
C_2 |
M |
175 |
74 |
47.2 |
B- |
street_2 |
S_1 |
C_1 |
F |
192 |
73 |
32.5 |
B+ |
|
|
C_1 |
M |
186 |
82 |
87.2 |
B+ |
df_muls.reorder_levels(['Address','School','Class'],axis=0).sort_index().head()
|
|
|
Gender |
Height |
Weight |
Math |
Physics |
Address |
School |
Class |
|
|
|
|
|
street_1 |
S_1 |
C_1 |
M |
173 |
63 |
34 |
A+ |
|
|
C_3 |
F |
175 |
57 |
87.7 |
A- |
|
S_2 |
C_2 |
M |
175 |
74 |
47.2 |
B- |
street_2 |
S_1 |
C_1 |
F |
192 |
73 |
32.5 |
B+ |
|
|
C_1 |
M |
186 |
82 |
87.2 |
B+ |
3 索引设定
3.1 index_col参数
index_col是read_csv中的一个参数,而不是某一个方法:
pd.read_csv('data/table.csv',index_col=['Address','School']).head()
|
Class |
ID |
Gender |
Height |
Weight |
Math |
Physics |
|
Address |
School |
|
|
|
|
|
|
|
street_1 |
S_1 |
C_1 |
1101 |
M |
173 |
63 |
34 |
A+ |
street_2 |
S_1 |
C_1 |
1102 |
F |
192 |
73 |
32.5 |
B+ |
|
S_1 |
C_1 |
1103 |
M |
186 |
82 |
87.2 |
B+ |
|
S_1 |
C_1 |
1104 |
F |
167 |
81 |
80.4 |
B- |
street_4 |
S_1 |
C_1 |
1105 |
F |
159 |
64 |
84.8 |
B+ |
3.2 reindex和reindex_like
reindex是指重新索引,它的重要特性在于索引对齐,很多时候用于重新排序
df.head()
|
School |
Class |
Gender |
Address |
Height |
Weight |
Math |
Physics |
ID |
|
|
|
|
|
|
|
|
1101 |
S_1 |
C_1 |
M |
street_1 |
173 |
63 |
34.0 |
A+ |
1102 |
S_1 |
C_1 |
F |
street_2 |
192 |
73 |
32.5 |
B+ |
1103 |
S_1 |
C_1 |
M |
street_2 |
186 |
82 |
87.2 |
B+ |
1104 |
S_1 |
C_1 |
F |
street_2 |
167 |
81 |
80.4 |
B- |
1105 |
S_1 |
C_1 |
F |
street_4 |
159 |
64 |
84.8 |
B+ |
df.reindex(index=[1101,1203,1206,2402])
|
School |
Class |
Gender |
Address |
Height |
Weight |
Math |
Physics |
ID |
|
|
|
|
|
|
|
|
1101 |
S_1 |
C_1 |
M |
street_1 |
173.0 |
63.0 |
34.0 |
A+ |
1203 |
S_1 |
C_2 |
M |
street_6 |
160.0 |
53.0 |
58.8 |
A+ |
1206 |
NaN |
NaN |
NaN |
NaN |
NaN |
NaN |
NaN |
NaN |
2402 |
S_2 |
C_4 |
M |
street_7 |
166.0 |
82.0 |
48.7 |
B |
df.reindex(columns=['Height','Gender','Average']).head()
|
Height |
Gender |
Average |
ID |
|
|
|
1101 |
173 |
M |
NaN |
1102 |
192 |
F |
NaN |
1103 |
186 |
M |
NaN |
1104 |
167 |
F |
NaN |
1105 |
159 |
F |
NaN |
可以选择缺失值的填充方法:fill_value和method(bfill/ffill/nearest),其中method参数必须索引单调。
df.reindex(index=[1101,1203,1206,2402],method='bfill')
|
School |
Class |
Gender |
Address |
Height |
Weight |
Math |
Physics |
ID |
|
|
|
|
|
|
|
|
1101 |
S_1 |
C_1 |
M |
street_1 |
173 |
63 |
34.0 |
A+ |
1203 |
S_1 |
C_2 |
M |
street_6 |
160 |
53 |
58.8 |
A+ |
1206 |
S_1 |
C_3 |
M |
street_4 |
161 |
68 |
31.5 |
B+ |
2402 |
S_2 |
C_4 |
M |
street_7 |
166 |
82 |
48.7 |
B |
df.reindex(index=[1101,1203,1206,2402],method='nearest')
|
School |
Class |
Gender |
Address |
Height |
Weight |
Math |
Physics |
ID |
|
|
|
|
|
|
|
|
1101 |
S_1 |
C_1 |
M |
street_1 |
173 |
63 |
34.0 |
A+ |
1203 |
S_1 |
C_2 |
M |
street_6 |
160 |
53 |
58.8 |
A+ |
1206 |
S_1 |
C_2 |
F |
street_6 |
167 |
63 |
68.4 |
B- |
2402 |
S_2 |
C_4 |
M |
street_7 |
166 |
82 |
48.7 |
B |
reindex_like的作用为生成一个横纵索引完全与参数列表一致的DataFrame,数据使用被调用的表
df_temp = pd.DataFrame({'Weight':np.zeros(5),
'Height':np.zeros(5),
'ID':[1101,1104,1103,1106,1102]}).set_index('ID')
df_temp.reindex_like(df[0:5][['Weight','Height']])
|
Weight |
Height |
ID |
|
|
1101 |
0.0 |
0.0 |
1102 |
0.0 |
0.0 |
1103 |
0.0 |
0.0 |
1104 |
0.0 |
0.0 |
1105 |
NaN |
NaN |
如果df_temp单调还可以使用method参数:
df_temp = pd.DataFrame({'Weight':range(5),
'Height':range(5),
'ID':[1101,1104,1103,1106,1102]}).set_index('ID').sort_index()
df_temp.reindex_like(df[0:5][['Weight','Height']],method='bfill')
|
Weight |
Height |
ID |
|
|
1101 |
0 |
0 |
1102 |
4 |
4 |
1103 |
2 |
2 |
1104 |
1 |
1 |
1105 |
3 |
3 |
3.3 set_index和reset_index
et_index:从字面意思看,就是将某些列作为索引
使用表内列作为索引:
df.head()
|
School |
Class |
Gender |
Address |
Height |
Weight |
Math |
Physics |
ID |
|
|
|
|
|
|
|
|
1101 |
S_1 |
C_1 |
M |
street_1 |
173 |
63 |
34.0 |
A+ |
1102 |
S_1 |
C_1 |
F |
street_2 |
192 |
73 |
32.5 |
B+ |
1103 |
S_1 |
C_1 |
M |
street_2 |
186 |
82 |
87.2 |
B+ |
1104 |
S_1 |
C_1 |
F |
street_2 |
167 |
81 |
80.4 |
B- |
1105 |
S_1 |
C_1 |
F |
street_4 |
159 |
64 |
84.8 |
B+ |
df.set_index('Class').head()
|
School |
Gender |
Address |
Height |
Weight |
Math |
Physics |
Class |
|
|
|
|
|
|
|
C_1 |
S_1 |
M |
street_1 |
173 |
63 |
34.0 |
A+ |
C_1 |
S_1 |
F |
street_2 |
192 |
73 |
32.5 |
B+ |
C_1 |
S_1 |
M |
street_2 |
186 |
82 |
87.2 |
B+ |
C_1 |
S_1 |
F |
street_2 |
167 |
81 |
80.4 |
B- |
C_1 |
S_1 |
F |
street_4 |
159 |
64 |
84.8 |
B+ |
利用append参数可以将当前索引维持不变
df.set_index('Class',append=True).head()
|
|
School |
Gender |
Address |
Height |
Weight |
Math |
Physics |
ID |
Class |
|
|
|
|
|
|
|
1101 |
C_1 |
S_1 |
M |
street_1 |
173 |
63 |
34.0 |
A+ |
1102 |
C_1 |
S_1 |
F |
street_2 |
192 |
73 |
32.5 |
B+ |
1103 |
C_1 |
S_1 |
M |
street_2 |
186 |
82 |
87.2 |
B+ |
1104 |
C_1 |
S_1 |
F |
street_2 |
167 |
81 |
80.4 |
B- |
1105 |
C_1 |
S_1 |
F |
street_4 |
159 |
64 |
84.8 |
|
当使用与表长相同的列作为索引(需要先转化为Series,否则报错):
df.set_index(pd.Series(range(df.shape[0]))).head()
|
School |
Class |
Gender |
Address |
Height |
Weight |
Math |
Physics |
0 |
S_1 |
C_1 |
M |
street_1 |
173 |
63 |
34.0 |
A+ |
1 |
S_1 |
C_1 |
F |
street_2 |
192 |
73 |
32.5 |
B+ |
2 |
S_1 |
C_1 |
M |
street_2 |
186 |
82 |
87.2 |
B+ |
3 |
S_1 |
C_1 |
F |
street_2 |
167 |
81 |
80.4 |
B- |
4 |
S_1 |
C_1 |
F |
street_4 |
159 |
64 |
84.8 |
B+ |
可以直接添加多级索引:
df.set_index([pd.Series(range(df.shape[0])),pd.Series(np.ones(df.shape[0]))]).head()
|
|
School |
Class |
Gender |
Address |
Height |
Weight |
Math |
Physics |
0 |
1.0 |
S_1 |
C_1 |
M |
street_1 |
173 |
63 |
34.0 |
A+ |
1 |
1.0 |
S_1 |
C_1 |
F |
street_2 |
192 |
73 |
32.5 |
B+ |
2 |
1.0 |
S_1 |
C_1 |
M |
street_2 |
186 |
82 |
87.2 |
B+ |
3 |
1.0 |
S_1 |
C_1 |
F |
street_2 |
167 |
81 |
80.4 |
B- |
4 |
1.0 |
S_1 |
C_1 |
F |
street_4 |
159 |
64 |
84.8 |
B+ |
reset_index方法,它的主要功能是将索引重置
默认状态直接恢复到自然数索引:
df.reset_index().head()
|
ID |
School |
Class |
Gender |
Address |
Height |
Weight |
Math |
Physics |
0 |
1101 |
S_1 |
C_1 |
M |
street_1 |
173 |
63 |
34.0 |
A+ |
1 |
1102 |
S_1 |
C_1 |
F |
street_2 |
192 |
73 |
32.5 |
B+ |
2 |
1103 |
S_1 |
C_1 |
M |
street_2 |
186 |
82 |
87.2 |
B+ |
3 |
1104 |
S_1 |
C_1 |
F |
street_2 |
167 |
81 |
80.4 |
B- |
4 |
1105 |
S_1 |
C_1 |
F |
street_4 |
159 |
64 |
84.8 |
B+ |
用level参数指定哪一层被reset,用col_level参数指定set到哪一层:
L1,L2 = ['A','B','C'],['a','b','c']
mul_index1 = pd.MultiIndex.from_product([L1,L2],names=('Upper', 'Lower'))
L3,L4 = ['D','E','F'],['d','e','f']
mul_index2 = pd.MultiIndex.from_product([L3,L4],names=('Big', 'Small'))
df_temp = pd.DataFrame(np.random.rand(9,9),index=mul_index1,columns=mul_index2)
df_temp.head()
Big |
|
|
|
D |
|
|
E |
|
|
F |
Small |
|
d |
e |
f |
d |
e |
f |
d |
e |
f |
Upper |
Lower |
|
|
|
|
|
|
|
|
|
A |
a |
0.415195 |
0.399841 |
0.432031 |
0.268736 |
0.148571 |
0.972363 |
0.89448 |
0.15669 |
0.462923 |
|
b |
0.490508 |
0.150571 |
0.10015 |
0.772613 |
0.847422 |
0.320051 |
0.550675 |
0.069499 |
0.191721 |
|
c |
0.193515 |
0.069548 |
0.720209 |
0.180638 |
0.988839 |
0.111657 |
0.649108 |
0.529743 |
0.739764 |
B |
a |
0.956325 |
0.139672 |
0.631007 |
0.704335 |
0.104828 |
0.262378 |
0.607194 |
0.725691 |
0.096959 |
|
b |
0.465611 |
0.288648 |
0.236706 |
0.706129 |
0.298313 |
0.342365 |
0.543323 |
0.490258 |
0.027482 |
df_temp1 = df_temp.reset_index(level=1,col_level=1)
df_temp1.head()
Big |
|
|
|
D |
|
|
E |
|
|
F |
Small |
Lower |
d |
e |
f |
d |
e |
f |
d |
e |
f |
Upper |
|
|
|
|
|
|
|
|
|
|
A |
a |
0.455772 |
0.568383 |
0.36601 |
0.142834 |
0.232744 |
0.045931 |
0.85495 |
0.082319 |
0.80917 |
A |
b |
0.446874 |
0.459203 |
0.49244 |
0.891093 |
0.619426 |
0.127137 |
0.136137 |
0.111108 |
0.424913 |
A |
c |
0.6719 |
0.195127 |
0.175704 |
0.940491 |
0.017882 |
0.195829 |
0.844949 |
0.335865 |
0.55247 |
B |
a |
0.114634 |
0.973796 |
0.847149 |
0.606002 |
0.939 |
0.773361 |
0.52839 |
0.700832 |
0.516844 |
B |
b |
0.683624 |
0.544524 |
0.904016 |
0.518869 |
0.839697 |
0.834856 |
0.874863 |
0.766719 |
0.598977 |
df_temp1.columns
MultiIndex([( '', 'Lower'),
('D', 'd'),
('D', 'e'),
('D', 'f'),
('E', 'd'),
('E', 'e'),
('E', 'f'),
('F', 'd'),
('F', 'e'),
('F', 'f')],
names=['Big', 'Small'])
df_temp1.index
Index(['A', 'A', 'A', 'B', 'B', 'B', 'C', 'C', 'C'], dtype='object', name='Upper')
3.4 rename_axis和rename
rename_axis是针对多级索引的方法,作用是修改某一层的索引名,而不是索引标签
df_temp.rename_axis(index={'Lower':'LowerLower'},columns={'Big':'BigBig'})
BigBig |
|
|
D |
|
|
E |
|
|
F |
|
Small |
|
d |
e |
f |
d |
e |
f |
d |
e |
f |
Upper |
LowerLower |
|
|
|
|
|
|
|
|
|
A |
a |
0.025169 |
0.113144 |
0.118285 |
0.775066 |
0.801492 |
0.497375 |
0.958616 |
0.685357 |
0.549634 |
|
b |
0.837498 |
0.337893 |
0.231633 |
0.831686 |
0.716031 |
0.626049 |
0.619013 |
0.877352 |
0.310406 |
|
c |
0.115737 |
0.111587 |
0.922571 |
0.258403 |
0.64657 |
0.936869 |
0.893763 |
0.014768 |
0.533456 |
B |
a |
0.024406 |
0.15918 |
0.530797 |
0.312714 |
0.230486 |
0.310252 |
0.695073 |
0.195527 |
0.302385 |
|
b |
0.453045 |
0.441613 |
0.327158 |
0.55987 |
0.951331 |
0.903411 |
0.406168 |
0.586651 |
0.284886 |
|
c |
0.66042 |
0.719856 |
0.860304 |
0.064605 |
0.331111 |
0.163686 |
0.920732 |
0.409673 |
0.219974 |
C |
a |
0.684049 |
0.900708 |
0.870861 |
0.044754 |
0.026487 |
0.146095 |
0.648923 |
0.187175 |
0.704501 |
|
b |
0.237486 |
0.6841 |
0.255666 |
0.166265 |
0.401716 |
0.040835 |
0.914865 |
0.696318 |
0.653498 |
|
c |
0.559561 |
0.044497 |
0.803069 |
0.374056 |
0.688914 |
0.56057 |
0.29154 |
0.705021 |
0.60011 |
rename方法用于修改列或者行索引标签,而不是索引名:
df_temp.rename(index={'A':'T'},columns={'e':'changed_e'}).head()
Big |
|
|
|
D |
|
|
E |
|
|
F |
Small |
|
d |
changed_e |
f |
d |
changed_e |
f |
d |
changed_e |
f |
Upper |
Lower |
|
|
|
|
|
|
|
|
|
T |
a |
0.967945 |
0.10047 |
0.592643 |
0.192416 |
0.990223 |
0.098881 |
0.198654 |
0.422801 |
0.304565 |
|
b |
0.326164 |
0.289546 |
0.829121 |
0.761338 |
0.008772 |
0.738461 |
0.340697 |
0.513727 |
0.385448 |
|
c |
0.475534 |
0.513195 |
0.825845 |
0.665717 |
0.359606 |
0.207218 |
0.55601 |
0.09565 |
0.880627 |
B |
a |
0.75757 |
0.872631 |
0.08105 |
0.52173 |
0.7818 |
0.84037 |
0.649206 |
0.577388 |
0.0943 |
|
b |
0.991114 |
0.033176 |
0.392372 |
0.590603 |
0.607997 |
0.171789 |
0.036382 |
0.106561 |
0.893742 |
4 常用索引型函数
4.1 where函数
当对条件为False的单元进行填充:
df.where(df['Gender']=='M').head()
|
School |
Class |
Gender |
Address |
Height |
Weight |
Math |
Physics |
ID |
|
|
|
|
|
|
|
|
1101 |
S_1 |
C_1 |
M |
street_1 |
173.0 |
63.0 |
34.0 |
A+ |
1102 |
NaN |
NaN |
NaN |
NaN |
NaN |
NaN |
NaN |
NaN |
1103 |
S_1 |
C_1 |
M |
street_2 |
186.0 |
82.0 |
87.2 |
B+ |
1104 |
NaN |
NaN |
NaN |
NaN |
NaN |
NaN |
NaN |
NaN |
1105 |
NaN |
NaN |
NaN |
NaN |
NaN |
NaN |
NaN |
NaN |
通过这种方法筛选结果和[]操作符的结果完全一致:
df.where(df['Gender']=='M').dropna().head()
|
School |
Class |
Gender |
Address |
Height |
Weight |
Math |
Physics |
ID |
|
|
|
|
|
|
|
|
1101 |
S_1 |
C_1 |
M |
street_1 |
173.0 |
63.0 |
34.0 |
A+ |
1103 |
S_1 |
C_1 |
M |
street_2 |
186.0 |
82.0 |
87.2 |
B+ |
1201 |
S_1 |
C_2 |
M |
street_5 |
188.0 |
68.0 |
97.0 |
A- |
1203 |
S_1 |
C_2 |
M |
street_6 |
160.0 |
53.0 |
58.8 |
A+ |
1301 |
S_1 |
C_3 |
M |
street_4 |
161.0 |
68.0 |
31.5 |
B+ |
第一个参数为布尔条件,第二个参数为填充值:
df.where(df['Gender']=='M',np.random.rand(df.shape[0],df.shape[1])).head()
|
School |
Class |
Gender |
Address |
Height |
Weight |
Math |
Physics |
ID |
|
|
|
|
|
|
|
|
1101 |
S_1 |
C_1 |
M |
street_1 |
173.000000 |
63.000000 |
34.000000 |
A+ |
1102 |
0.0152467 |
0.708444 |
0.917199 |
0.302185 |
0.689643 |
0.010126 |
0.724636 |
0.895387 |
1103 |
S_1 |
C_1 |
M |
street_2 |
186.000000 |
82.000000 |
87.200000 |
B+ |
1104 |
0.369195 |
0.459211 |
0.464191 |
0.964486 |
0.365797 |
0.127602 |
0.501496 |
0.0287754 |
1105 |
0.812232 |
0.999634 |
0.825782 |
0.285692 |
0.340197 |
0.083982 |
0.792310 |
0.133054 |
4.2 mask函数
mask函数与where功能上相反,其余完全一致,即对条件为True的单元进行填充
df.mask(df['Gender']=='M').dropna().head()
|
School |
Class |
Gender |
Address |
Height |
Weight |
Math |
Physics |
ID |
|
|
|
|
|
|
|
|
1102 |
S_1 |
C_1 |
F |
street_2 |
192.0 |
73.0 |
32.5 |
B+ |
1104 |
S_1 |
C_1 |
F |
street_2 |
167.0 |
81.0 |
80.4 |
B- |
1105 |
S_1 |
C_1 |
F |
street_4 |
159.0 |
64.0 |
84.8 |
B+ |
1202 |
S_1 |
C_2 |
F |
street_4 |
176.0 |
94.0 |
63.5 |
B- |
1204 |
S_1 |
C_2 |
F |
street_5 |
162.0 |
63.0 |
33.8 |
B |
df.mask(df['Gender']=='M',np.random.rand(df.shape[0],df.shape[1])).head()
|
School |
Class |
Gender |
Address |
Height |
Weight |
Math |
Physics |
ID |
|
|
|
|
|
|
|
|
1101 |
0.273962 |
0.25028 |
0.587471 |
0.977206 |
0.442403 |
0.319460 |
0.460991 |
0.842498 |
1102 |
S_1 |
C_1 |
F |
street_2 |
192.000000 |
73.000000 |
32.500000 |
B+ |
1103 |
0.436674 |
0.741524 |
0.46996 |
0.688603 |
0.938241 |
0.531811 |
0.794352 |
0.17495 |
1104 |
S_1 |
C_1 |
F |
street_2 |
167.000000 |
81.000000 |
80.400000 |
B- |
1105 |
S_1 |
C_1 |
F |
street_4 |
159.000000 |
64.000000 |
84.800000 |
B+ |
4.3 query函数
query函数中的布尔表达式中,下面的符号都是合法的:行列索引名、字符串、and/not/or/&/|/~/not in/in/==/!=、四则运算符
df.query('(Address in ["street_6","street_7"])&(Weight>(70+10))&(ID in [1303,2304,2402])')
|
School |
Class |
Gender |
Address |
Height |
Weight |
Math |
Physics |
ID |
|
|
|
|
|
|
|
|
1303 |
S_1 |
C_3 |
M |
street_7 |
188 |
82 |
49.7 |
B |
2304 |
S_2 |
C_3 |
F |
street_6 |
164 |
81 |
95.5 |
A- |
2402 |
S_2 |
C_4 |
M |
street_7 |
166 |
82 |
48.7 |
B |
5 重复元素处理
5.1 duplicated方法
该方法返回了是否重复的布尔列表
df.duplicated('Class').head()
ID
1101 False
1102 True
1103 True
1104 True
1105 True
dtype: bool
可选参数keep默认为first,即首次出现设为不重复,若为last,则最后一次设为不重复,若为False,则所有重复项为False
df.duplicated('Class',keep='last').tail()
ID
2401 True
2402 True
2403 True
2404 True
2405 False
dtype: bool
df.duplicated('Class',keep=False).head()
ID
1101 True
1102 True
1103 True
1104 True
1105 True
dtype: bool
5.2 drop_duplicates方法
剔除重复项
df.drop_duplicates('Class')
|
School |
Class |
Gender |
Address |
Height |
Weight |
Math |
Physics |
ID |
|
|
|
|
|
|
|
|
1101 |
S_1 |
C_1 |
M |
street_1 |
173 |
63 |
34.0 |
A+ |
1201 |
S_1 |
C_2 |
M |
street_5 |
188 |
68 |
97.0 |
A- |
1301 |
S_1 |
C_3 |
M |
street_4 |
161 |
68 |
31.5 |
B+ |
2401 |
S_2 |
C_4 |
F |
street_2 |
192 |
62 |
45.3 |
A |
参数与duplicate函数类似:
df.drop_duplicates('Class',keep='last')
|
School |
Class |
Gender |
Address |
Height |
Weight |
Math |
Physics |
ID |
|
|
|
|
|
|
|
|
2105 |
S_2 |
C_1 |
M |
street_4 |
170 |
81 |
34.2 |
A |
2205 |
S_2 |
C_2 |
F |
street_7 |
183 |
76 |
85.4 |
B |
2305 |
S_2 |
C_3 |
M |
street_4 |
187 |
73 |
48.9 |
B |
2405 |
S_2 |
C_4 |
F |
street_6 |
193 |
54 |
47.6 |
B |
在传入多列时等价于将多列共同视作一个多级索引,比较重复项:
df.drop_duplicates(['School','Class'])
|
School |
Class |
Gender |
Address |
Height |
Weight |
Math |
Physics |
ID |
|
|
|
|
|
|
|
|
1101 |
S_1 |
C_1 |
M |
street_1 |
173 |
63 |
34.0 |
A+ |
1201 |
S_1 |
C_2 |
M |
street_5 |
188 |
68 |
97.0 |
A- |
1301 |
S_1 |
C_3 |
M |
street_4 |
161 |
68 |
31.5 |
B+ |
2101 |
S_2 |
C_1 |
M |
street_7 |
174 |
84 |
83.3 |
C |
2201 |
S_2 |
C_2 |
M |
street_5 |
193 |
100 |
39.1 |
B |
2301 |
S_2 |
C_3 |
F |
street_4 |
157 |
78 |
72.3 |
B+ |
2401 |
S_2 |
C_4 |
F |
street_2 |
192 |
62 |
45.3 |
A |
6 抽样函数
这里的抽样函数指的就是sample函数
6.1 n为样本量
df.sample(n=5)
|
School |
Class |
Gender |
Address |
Height |
Weight |
Math |
Physics |
ID |
|
|
|
|
|
|
|
|
2103 |
S_2 |
C_1 |
M |
street_4 |
157 |
61 |
52.5 |
B- |
1102 |
S_1 |
C_1 |
F |
street_2 |
192 |
73 |
32.5 |
B+ |
1301 |
S_1 |
C_3 |
M |
street_4 |
161 |
68 |
31.5 |
B+ |
1304 |
S_1 |
C_3 |
M |
street_2 |
195 |
70 |
85.2 |
A |
1105 |
S_1 |
C_1 |
F |
street_4 |
159 |
64 |
84.8 |
B+ |
6.2 frac为抽样比
df.sample(frac=0.05)
|
School |
Class |
Gender |
Address |
Height |
Weight |
Math |
Physics |
ID |
|
|
|
|
|
|
|
|
1105 |
S_1 |
C_1 |
F |
street_4 |
159 |
64 |
84.8 |
B+ |
2402 |
S_2 |
C_4 |
M |
street_7 |
166 |
82 |
48.7 |
B |
6.3 replace为是否放回
df.sample(n=df.shape[0],replace=True).head()
|
School |
Class |
Gender |
Address |
Height |
Weight |
Math |
Physics |
ID |
|
|
|
|
|
|
|
|
2403 |
S_2 |
C_4 |
F |
street_6 |
158 |
60 |
59.7 |
B+ |
2404 |
S_2 |
C_4 |
F |
street_2 |
160 |
84 |
67.7 |
B |
2405 |
S_2 |
C_4 |
F |
street_6 |
193 |
54 |
47.6 |
B |
2303 |
S_2 |
C_3 |
F |
street_7 |
190 |
99 |
65.9 |
C |
1203 |
S_1 |
C_2 |
M |
street_6 |
160 |
53 |
58.8 |
A+ |
df.sample(n=35,replace=True).index.is_unique
False
6.4 axis为抽样维度,默认为0,即抽行
df.sample(n=3,axis=1).head()
|
Address |
Weight |
School |
ID |
|
|
|
1101 |
street_1 |
63 |
S_1 |
1102 |
street_2 |
73 |
S_1 |
1103 |
street_2 |
82 |
S_1 |
1104 |
street_2 |
81 |
S_1 |
1105 |
street_4 |
64 |
S_1 |
6.5 weights为样本权重,自动归一化
df.sample(n=3,weights=np.random.rand(df.shape[0])).head()
|
School |
Class |
Gender |
Address |
Height |
Weight |
Math |
Physics |
ID |
|
|
|
|
|
|
|
|
1302 |
S_1 |
C_3 |
F |
street_1 |
175 |
57 |
87.7 |
A- |
1305 |
S_1 |
C_3 |
F |
street_5 |
187 |
69 |
61.7 |
B- |
2404 |
S_2 |
C_4 |
F |
street_2 |
160 |
84 |
67.7 |
B |
df.sample(n=3,weights=df['Math']).head()
|
School |
Class |
Gender |
Address |
Height |
Weight |
Math |
Physics |
ID |
|
|
|
|
|
|
|
|
1305 |
S_1 |
C_3 |
F |
street_5 |
187 |
69 |
61.7 |
B- |
2103 |
S_2 |
C_1 |
M |
street_4 |
157 |
61 |
52.5 |
B- |
2105 |
S_2 |
C_1 |
M |
street_4 |
170 |
81 |
34.2 |
A |