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pandas使用

pandas使用

pandas是python字典和numpy的结合,它的每一行每一列都可以赋予一个名字,其真正的数据则是numpy数据。

它的主要数据结构是Series(一维数据)与DataFrame(二维数据)。

基本介绍

import pandas as pd
import numpy as np

# 定义一维数据
s = pd.Series([1,3,6,np.nan,44,1])
print(s)
# 定义日期的数据
dates = pd.date_range('20220318',periods=6)
print(dates)
# 定义二维数据,指定行索引index和列索引columns
df = pd.DataFrame(np.random.randn(6,4),index=dates,columns=['a','b','c','d'])
print(df)
# 定义二维数据,使用默认索引
df1 = pd.DataFrame(np.arange(12).reshape(3,4))
print(df1)
# 用字典定义DataFrame
df2 = pd.DataFrame({
    'A':1.,
    'B':pd.Timestamp('20220318'),
    'C':pd.Series(1,index=list(range(4)),dtype='float32'),
    'D':np.array([3]*4,dtype='int32'),
    'E':pd.Categorical(["test","train","test","train"]),
    'F':'foo'
})
print(df2)
# DataFrame的属性
print(df2.dtypes)
print(df2.index)
print(df2.columns)
print(df2.values)
print(df2.describe()) # 计算values中数字数据的统计数据

print(df2.T) # 转置

# 按照index进行顺序
print(df2.sort_index(axis=1,ascending=False))
print(df2.sort_index(axis=0,ascending=False))
# 按照values进行排序
print(df2.sort_values(by='E'))
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结果:

0     1.0
1     3.0
2     6.0
3     NaN
4    44.0
5     1.0
dtype: float64
DatetimeIndex(['2022-03-18', '2022-03-19', '2022-03-20', '2022-03-21',
               '2022-03-22', '2022-03-23'],
              dtype='datetime64[ns]', freq='D')
                   a         b         c         d
2022-03-18 -0.686373  0.975663 -0.164654 -0.134341
2022-03-19  0.721421  2.056876  0.012457 -1.293365
2022-03-20  0.484431 -0.786625  1.069571  1.466806
2022-03-21  0.912695  0.488881 -0.733907  0.868177
2022-03-22 -0.406071 -2.308976  1.377417 -0.423213
2022-03-23  0.961852 -0.734838  1.221765 -2.290225
   0  1   2   3
0  0  1   2   3
1  4  5   6   7
2  8  9  10  11
     A          B    C  D      E    F
0  1.0 2022-03-18  1.0  3   test  foo
1  1.0 2022-03-18  1.0  3  train  foo
2  1.0 2022-03-18  1.0  3   test  foo
3  1.0 2022-03-18  1.0  3  train  foo
A           float64
B    datetime64[ns]
C           float32
D             int32
E          category
F            object
dtype: object
Int64Index([0, 1, 2, 3], dtype='int64')
Index(['A', 'B', 'C', 'D', 'E', 'F'], dtype='object')
[[1.0 Timestamp('2022-03-18 00:00:00') 1.0 3 'test' 'foo']
 [1.0 Timestamp('2022-03-18 00:00:00') 1.0 3 'train' 'foo']
 [1.0 Timestamp('2022-03-18 00:00:00') 1.0 3 'test' 'foo']
 [1.0 Timestamp('2022-03-18 00:00:00') 1.0 3 'train' 'foo']]
         A    C    D
count  4.0  4.0  4.0
mean   1.0  1.0  3.0
std    0.0  0.0  0.0
min    1.0  1.0  3.0
25%    1.0  1.0  3.0
50%    1.0  1.0  3.0
75%    1.0  1.0  3.0
max    1.0  1.0  3.0
                     0  ...                    3
A                    1  ...                    1
B  2022-03-18 00:00:00  ...  2022-03-18 00:00:00
C                    1  ...                    1
D                    3  ...                    3
E                 test  ...                train
F                  foo  ...                  foo

[6 rows x 4 columns]
     F      E  D    C          B    A
0  foo   test  3  1.0 2022-03-18  1.0
1  foo  train  3  1.0 2022-03-18  1.0
2  foo   test  3  1.0 2022-03-18  1.0
3  foo  train  3  1.0 2022-03-18  1.0
     A          B    C  D      E    F
3  1.0 2022-03-18  1.0  3  train  foo
2  1.0 2022-03-18  1.0  3   test  foo
1  1.0 2022-03-18  1.0  3  train  foo
0  1.0 2022-03-18  1.0  3   test  foo
     A          B    C  D      E    F
0  1.0 2022-03-18  1.0  3   test  foo
2  1.0 2022-03-18  1.0  3   test  foo
1  1.0 2022-03-18  1.0  3  train  foo
3  1.0 2022-03-18  1.0  3  train  foo
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pandas选择数据

import pandas as pd
import numpy as np

dates = pd.date_range('20220318',periods=6)
df = pd.DataFrame(np.arange(24).reshape((6,4)),index=dates,columns=['A','B','C','D'])

print(df)
# 索引列
print(df['A'],df.A)
print(df[0:3],df['20220319':'20220321'])

# 用label来筛选 loc
print(df.loc['20220322'])
print(df.loc[:,['A','B']])

# 用位置来筛选 iloc
print(df.iloc[3,1])
print(df.iloc[3:5,1:3])
print(df.iloc[[1,3,5],1:3])

# 条件筛选
print(df[df.A<8])
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结果:

             A   B   C   D
2022-03-18   0   1   2   3
2022-03-19   4   5   6   7
2022-03-20   8   9  10  11
2022-03-21  12  13  14  15
2022-03-22  16  17  18  19
2022-03-23  20  21  22  23
2022-03-18     0
2022-03-19     4
2022-03-20     8
2022-03-21    12
2022-03-22    16
2022-03-23    20
Freq: D, Name: A, dtype: int32 2022-03-18     0
2022-03-19     4
2022-03-20     8
2022-03-21    12
2022-03-22    16
2022-03-23    20
Freq: D, Name: A, dtype: int32
            A  B   C   D
2022-03-18  0  1   2   3
2022-03-19  4  5   6   7
2022-03-20  8  9  10  11              A   B   C   D
2022-03-19   4   5   6   7
2022-03-20   8   9  10  11
2022-03-21  12  13  14  15
A    16
B    17
C    18
D    19
Name: 2022-03-22 00:00:00, dtype: int32
             A   B
2022-03-18   0   1
2022-03-19   4   5
2022-03-20   8   9
2022-03-21  12  13
2022-03-22  16  17
2022-03-23  20  21
13
             B   C
2022-03-21  13  14
2022-03-22  17  18
             B   C
2022-03-19   5   6
2022-03-21  13  14
2022-03-23  21  22
            A  B  C  D
2022-03-18  0  1  2  3
2022-03-19  4  5  6  7
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pandas设置值

import pandas as pd
import numpy as np

dates = pd.date_range('20220318',periods=6)
df = pd.DataFrame(np.arange(24).reshape((6,4)),index=dates,columns=['A','B','C','D'])
print(df)
df.iloc[2,2] = 1111
df.loc['20220318'] = 2222
df.A[df.A>4] = 0
print(df)
# 添加一列
df['F'] = np.nan
print(df)
# 虽然添加了一列数字,但是显示全是NaN
df['E'] = pd.Series(np.array([1,2,3,4,5,6]))
print(df)
df['E'] = pd.Series(np.array([1,2,3,4,5,6]),index=dates)
print(df)
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结果:

             A   B   C   D
2022-03-18   0   1   2   3
2022-03-19   4   5   6   7
2022-03-20   8   9  10  11
2022-03-21  12  13  14  15
2022-03-22  16  17  18  19
2022-03-23  20  21  22  23
            A     B     C     D
2022-03-18  0  2222  2222  2222
2022-03-19  4     5     6     7
2022-03-20  0     9  1111    11
2022-03-21  0    13    14    15
2022-03-22  0    17    18    19
2022-03-23  0    21    22    23
            A     B     C     D   F
2022-03-18  0  2222  2222  2222 NaN
2022-03-19  4     5     6     7 NaN
2022-03-20  0     9  1111    11 NaN
2022-03-21  0    13    14    15 NaN
2022-03-22  0    17    18    19 NaN
2022-03-23  0    21    22    23 NaN
            A     B     C     D   F   E
2022-03-18  0  2222  2222  2222 NaN NaN
2022-03-19  4     5     6     7 NaN NaN
2022-03-20  0     9  1111    11 NaN NaN
2022-03-21  0    13    14    15 NaN NaN
2022-03-22  0    17    18    19 NaN NaN
2022-03-23  0    21    22    23 NaN NaN
            A     B     C     D   F  E
2022-03-18  0  2222  2222  2222 NaN  1
2022-03-19  4     5     6     7 NaN  2
2022-03-20  0     9  1111    11 NaN  3
2022-03-21  0    13    14    15 NaN  4
2022-03-22  0    17    18    19 NaN  5
2022-03-23  0    21    22    23 NaN  6
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pandas处理丢失数据

import pandas as pd
import numpy as np

dates = pd.date_range('20220318',periods=6)
df = pd.DataFrame(np.arange(24).reshape((6,4)),index=dates,columns=['A','B','C','D'])
df.iloc[0,1] = np.nan
df.iloc[1,2] = np.nan
print(df)

# 丢掉nan所在的列
print(df.dropna(axis=1,how='any')) # how={'any','all'},默认是'any'
# 丢掉nan所在的行
print(df.dropna(axis=0,how='any'))
# 用零填充nan
print(df.fillna(value=0))
# 返回一个DataFrame,每个值都是bool,代表是否是nan
print(df.isnull())
# 判断是否有缺失数据
print(np.any(df.isnull())==True)
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结果:

             A     B     C   D
2022-03-18   0   NaN   2.0   3
2022-03-19   4   5.0   NaN   7
2022-03-20   8   9.0  10.0  11
2022-03-21  12  13.0  14.0  15
2022-03-22  16  17.0  18.0  19
2022-03-23  20  21.0  22.0  23
             A   D
2022-03-18   0   3
2022-03-19   4   7
2022-03-20   8  11
2022-03-21  12  15
2022-03-22  16  19
2022-03-23  20  23
             A     B     C   D
2022-03-20   8   9.0  10.0  11
2022-03-21  12  13.0  14.0  15
2022-03-22  16  17.0  18.0  19
2022-03-23  20  21.0  22.0  23
             A     B     C   D
2022-03-18   0   0.0   2.0   3
2022-03-19   4   5.0   0.0   7
2022-03-20   8   9.0  10.0  11
2022-03-21  12  13.0  14.0  15
2022-03-22  16  17.0  18.0  19
2022-03-23  20  21.0  22.0  23
                A      B      C      D
2022-03-18  False   True  False  False
2022-03-19  False  False   True  False
2022-03-20  False  False  False  False
2022-03-21  False  False  False  False
2022-03-22  False  False  False  False
2022-03-23  False  False  False  False
True
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pandas导入导出

在这里插入图片描述

在这里插入图片描述

import pandas as pd

# 会自动加上index
data = pd.read_csv('student.csv')
print(data)

data.to_pickle('student.pickle')
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结果:

原始数据如下图所示:

在这里插入图片描述

    Student ID  name   age  gender
0         1100  Kelly   22  Female
1         1101    Clo   21  Female
2         1102  Tilly   22  Female
3         1103   Tony   24    Male
4         1104  David   20    Male
5         1105  Catty   22  Female
6         1106      M    3  Female
7         1107      N   43    Male
8         1108      A   13    Male
9         1109      S   12    Male
10        1110  David   33    Male
11        1111     Dw    3  Female
12        1112      Q   23    Male
13        1113      W   21  Female
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pandas合并concat

import pandas as pd
import numpy as np

# concatenating
df1 = pd.DataFrame(np.ones((3,4))*0,columns=['a','b','c','d'])
df2 = pd.DataFrame(np.ones((3,4))*1,columns=['a','b','c','d'])
df3 = pd.DataFrame(np.ones((3,4))*2,columns=['a','b','c','d'])
print(df1)
print(df2)
print(df3)
# 保留原始index
res = pd.concat([df1,df2,df3],axis=0)
print(res)
# 忽略原始index,重新赋予index
res = pd.concat([df1,df2,df3],axis=0,ignore_index=True)
print(res)

# join,['inner','outer']
df1 = pd.DataFrame(np.ones((3,4))*0,index=[1,2,3],columns=['a','b','c','d'])
df2 = pd.DataFrame(np.ones((3,4))*1,index=[2,3,4],columns=['b','c','d','e'])
print(df1)
print(df2)
# 相当于两个的并集,不相互重合的地方会用nan填充
res = pd.concat([df1,df2],join='outer',ignore_index=True) # 默认是outer填充
print(res)
# 相当于两个的交集
res = pd.concat([df1,df2],join='inner',ignore_index=True)
print(res)

# 新版本pandas中按列合并只能用merge
df1 = pd.DataFrame(np.ones((3,4))*0,index=[1,2,3],columns=['a','b','c','d'])
df2 = pd.DataFrame(np.ones((3,4))*1,index=[2,3,4],columns=['b','c','d','e'])
# how {'inner','outer','left','right'}
res = pd.merge(df1,df2,how='left',left_index=True,right_index=True)
print(res)

# append 加数据
df1 = pd.DataFrame(np.ones((3,4))*0,columns=['a','b','c','d'])
df2 = pd.DataFrame(np.ones((3,4))*1,columns=['a','b','c','d'])
df3 = pd.DataFrame(np.ones((3,4))*1,columns=['a','b','c','d'])
res = df1.append([df2,df3],ignore_index=True)
print(res)

s1 = pd.Series([1,2,3,4],index=['a','b','c','d'])
res = df1.append(s1,ignore_index=True)
print(res)
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结果:

     a    b    c    d
0  0.0  0.0  0.0  0.0
1  0.0  0.0  0.0  0.0
2  0.0  0.0  0.0  0.0
     a    b    c    d
0  1.0  1.0  1.0  1.0
1  1.0  1.0  1.0  1.0
2  1.0  1.0  1.0  1.0
     a    b    c    d
0  2.0  2.0  2.0  2.0
1  2.0  2.0  2.0  2.0
2  2.0  2.0  2.0  2.0
     a    b    c    d
0  0.0  0.0  0.0  0.0
1  0.0  0.0  0.0  0.0
2  0.0  0.0  0.0  0.0
0  1.0  1.0  1.0  1.0
1  1.0  1.0  1.0  1.0
2  1.0  1.0  1.0  1.0
0  2.0  2.0  2.0  2.0
1  2.0  2.0  2.0  2.0
2  2.0  2.0  2.0  2.0
     a    b    c    d
0  0.0  0.0  0.0  0.0
1  0.0  0.0  0.0  0.0
2  0.0  0.0  0.0  0.0
3  1.0  1.0  1.0  1.0
4  1.0  1.0  1.0  1.0
5  1.0  1.0  1.0  1.0
6  2.0  2.0  2.0  2.0
7  2.0  2.0  2.0  2.0
8  2.0  2.0  2.0  2.0
     a    b    c    d
1  0.0  0.0  0.0  0.0
2  0.0  0.0  0.0  0.0
3  0.0  0.0  0.0  0.0
     b    c    d    e
2  1.0  1.0  1.0  1.0
3  1.0  1.0  1.0  1.0
4  1.0  1.0  1.0  1.0
     a    b    c    d    e
0  0.0  0.0  0.0  0.0  NaN
1  0.0  0.0  0.0  0.0  NaN
2  0.0  0.0  0.0  0.0  NaN
3  NaN  1.0  1.0  1.0  1.0
4  NaN  1.0  1.0  1.0  1.0
5  NaN  1.0  1.0  1.0  1.0
     b    c    d
0  0.0  0.0  0.0
1  0.0  0.0  0.0
2  0.0  0.0  0.0
3  1.0  1.0  1.0
4  1.0  1.0  1.0
5  1.0  1.0  1.0
     a  b_x  c_x  d_x  b_y  c_y  d_y    e
1  0.0  0.0  0.0  0.0  NaN  NaN  NaN  NaN
2  0.0  0.0  0.0  0.0  1.0  1.0  1.0  1.0
3  0.0  0.0  0.0  0.0  1.0  1.0  1.0  1.0
     a    b    c    d
0  0.0  0.0  0.0  0.0
1  0.0  0.0  0.0  0.0
2  0.0  0.0  0.0  0.0
3  1.0  1.0  1.0  1.0
4  1.0  1.0  1.0  1.0
5  1.0  1.0  1.0  1.0
6  1.0  1.0  1.0  1.0
7  1.0  1.0  1.0  1.0
8  1.0  1.0  1.0  1.0
     a    b    c    d
0  0.0  0.0  0.0  0.0
1  0.0  0.0  0.0  0.0
2  0.0  0.0  0.0  0.0
3  1.0  2.0  3.0  4.0
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pandas合并merge

import pandas as pd
import numpy as np

left = pd.DataFrame({'key':['K0','K1','K2','K3'],
                     'A':['A0','A1','A2','A3'],
                     'B':['B0','B1','B2','B3'],})
right = pd.DataFrame({'key':['K0','K1','K2','K3'],
                     'C':['C0','C1','C2','C3'],
                     'D':['D0','D1','D2','D3'],})
print(left)
print(right)
# merging two df by key/keys
res = pd.merge(left,right,on='key')
print(res)
# consider two keys
left = pd.DataFrame({'key1':['K0','K0','K1','K2'],
                     'key2':['K0','K1','K0','K1'],
                     'A':['A0','A1','A2','A3'],
                     'B':['B0','B1','B2','B3'],})
right = pd.DataFrame({'key1':['K0','K1','K1','K2'],
                      'key2':['K0','K0','K0','K0'],
                      'C':['C0','C1','C2','C3'],
                      'D':['D0','D1','D2','D3'],})
print(left)
print(right)
# left有一对(K1,K0),right有两对(K1,K0),inner方式合并就是把A那一对复制两遍进行合并
# how {'inner','outer','left','right'}, 默认是inner
res = pd.merge(left,right,on=['key1','key2'],how='inner')
print(res)
# how='outer',没有的就用nan
res = pd.merge(left,right,on=['key1','key2'],how='outer')
print(res)
# how='right',基于right进行合并,若left没有的就填充nan
res = pd.merge(left,right,on=['key1','key2'],how='right')
print(res)

df1 = pd.DataFrame({'col1':[0,1],'col_left':['a','b']})
df2 = pd.DataFrame({'col1':[1,2,2],'col_left':[2,2,2]})
print(df1)
print(df2)
# given the indicator a custom name
res = pd.merge(df1,df2,on='col1',how='outer',indicator=True)
print(res)
res = pd.merge(df1,df2,on='col1',how='outer',indicator='indicator_column')
print(res)

# merge by index
left = pd.DataFrame({'A':['A0','A1','A2'],
                    'B':['B0','B1','B2'],},
                   index=['K0','K1','K2'])
right = pd.DataFrame({'C':['C0','C1','C2'],
                    'D':['D0','D1','D2'],},
                   index=['K0','K1','K2'])
print(left)
print(right)
# left_index and right_index
res = pd.merge(left,right,left_index=True,right_index=True,how='outer')
print(res)

# handle overlapping
boys = pd.DataFrame({'k':['K0','K1','K2'],'age':[1,2,3]})
girls = pd.DataFrame({'k':['K0','K0','K3'],'age':[4,5,6]})
print(boys)
print(girls)
res = pd.merge(boys,girls,on='k',how='inner')
print(res)
res = pd.merge(boys,girls,on='k',how='inner',suffixes=['_boy','_girl']) # 设置同名key的后缀
print(res)
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结果:

  key   A   B
0  K0  A0  B0
1  K1  A1  B1
2  K2  A2  B2
3  K3  A3  B3
  key   C   D
0  K0  C0  D0
1  K1  C1  D1
2  K2  C2  D2
3  K3  C3  D3
  key   A   B   C   D
0  K0  A0  B0  C0  D0
1  K1  A1  B1  C1  D1
2  K2  A2  B2  C2  D2
3  K3  A3  B3  C3  D3
  key1 key2   A   B
0   K0   K0  A0  B0
1   K0   K1  A1  B1
2   K1   K0  A2  B2
3   K2   K1  A3  B3
  key1 key2   C   D
0   K0   K0  C0  D0
1   K1   K0  C1  D1
2   K1   K0  C2  D2
3   K2   K0  C3  D3
  key1 key2   A   B   C   D
0   K0   K0  A0  B0  C0  D0
1   K1   K0  A2  B2  C1  D1
2   K1   K0  A2  B2  C2  D2
  key1 key2    A    B    C    D
0   K0   K0   A0   B0   C0   D0
1   K0   K1   A1   B1  NaN  NaN
2   K1   K0   A2   B2   C1   D1
3   K1   K0   A2   B2   C2   D2
4   K2   K1   A3   B3  NaN  NaN
5   K2   K0  NaN  NaN   C3   D3
  key1 key2    A    B   C   D
0   K0   K0   A0   B0  C0  D0
1   K1   K0   A2   B2  C1  D1
2   K1   K0   A2   B2  C2  D2
3   K2   K0  NaN  NaN  C3  D3
   col1 col_left
0     0        a
1     1        b
   col1  col_left
0     1         2
1     2         2
2     2         2
   col1 col_left_x  col_left_y      _merge
0     0          a         NaN   left_only
1     1          b         2.0        both
2     2        NaN         2.0  right_only
3     2        NaN         2.0  right_only
   col1 col_left_x  col_left_y indicator_column
0     0          a         NaN        left_only
1     1          b         2.0             both
2     2        NaN         2.0       right_only
3     2        NaN         2.0       right_only
     A   B
K0  A0  B0
K1  A1  B1
K2  A2  B2
     C   D
K0  C0  D0
K1  C1  D1
K2  C2  D2
     A   B   C   D
K0  A0  B0  C0  D0
K1  A1  B1  C1  D1
K2  A2  B2  C2  D2
    k  age
0  K0    1
1  K1    2
2  K2    3
    k  age
0  K0    4
1  K0    5
2  K3    6
    k  age_x  age_y
0  K0      1      4
1  K0      1      5
    k  age_boy  age_girl
0  K0        1         4
1  K0        1         5
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pandas plot 绘图

import pandas as pd
import numpy as np
import matplotlib.pyplot as plt

# Series
data = pd.Series(np.random.randn(1000),index=np.arange(1000))
data = data.cumsum()
data.plot()

# DataFrame
data = pd.DataFrame(np.random.randn(1000,4),
                    index=np.arange(1000),
                    columns=list("ABCD"))
data = data.cumsum()
data.plot()
# plot methods: 'bar', 'hist','box','kde','area','scatter','hexbin','pie'
ax = data.plot.scatter(x='A',y='B',color='DarkBlue',label='Class 1')
data.plot.scatter(x='A',y='C',color='DarkGreen',label='Class 2',ax=ax)
plt.show()
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结果:

在这里插入图片描述
在这里插入图片描述
在这里插入图片描述
补充

【宝藏级】全网最全的Pandas详细教程(2万字总结)

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