Python pandas快速入门

r囧r小猫 2021-06-24 14:37 461阅读 0赞

[来自官网十分钟教学][Link 1]  
Pandas的主要数据结构：

<table> 
 <thead> 
  <tr> 
   <th>Dimensions</th> 
   <th align="center">Name</th> 
   <th align="right">Description</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>1</td> 
   <td align="center">Series</td> 
   <td align="right">1D labeled homogeneously-typed array</td> 
  </tr> 
  <tr> 
   <td>2</td> 
   <td align="center">DataFrame</td> 
   <td align="right">General 2D labeled, size-mutable tabular structure with potentially heterogeneously-typed columns</td> 
  </tr> 
  <tr> 
   <td>3</td> 
   <td align="center">Panel</td> 
   <td align="right">General 3D labeled, also size-mutable array</td> 
  </tr> 
 </tbody> 
</table>

## **一、引入** ##

import pandas as pd   //数据分析，代码基于numpy
    import numpy as np    //处理数据，代码基于ndarray
    import matplotlib.pyplot as plt      //画图

[matplotlib图库具有大量代码案例，可直接使用][matplotlib]  
[pandas 官网教程][pandas]

## **二、创建对象** ##

**Series字典对象**

>>>s = pd.Series([1,3,5,np.nan,6,8])   //默认以数字从0开始作为键值,使用np.nan表示不参与计算
    >>>s
    0    1.0
    1    3.0
    2    5.0
    3    NaN
    4    6.0
    5    8.0
    dtype: float64

>>> s = pd.Series(data=[1,2,3,4],index = ['a','b','c','d'])  //传入键和值方式
    >>> s
    a    1
    b    2
    c    3
    d    4
    dtype: int64
    >>> s.index    //获取键列表
    Index(['a', 'b', 'c', 'd'], dtype='object')
    >>> s.values    //获取值列表
    array([1, 2, 3, 4], dtype=int64)

**DataFrame表格对象**

In [10]: df2 = pd.DataFrame({ 'A' : 1.,
                         'B' : pd.Timestamp('20130102'),
                         'C' : pd.Series(1,index=list(range(4)),dtype='float32'),   //生成Series对象,取的是value
                         'D' : np.array([3] * 4,dtype='int32'),  //生成numpy对象
                         'E' : pd.Categorical(["test","train","test","train"]),
                         'F' : 'foo' })  
    
    
    In [11]: df2
    Out[11]:          // 默认以数字从0开始作为行键,以字典键为列键
         A          B    C  D      E    F
    0  1.0 2013-01-02  1.0  3   test  foo
    1  1.0 2013-01-02  1.0  3  train  foo
    2  1.0 2013-01-02  1.0  3   test  foo
    3  1.0 2013-01-02  1.0  3  train  foo

In [6]: dates = pd.date_range('20130101', periods=6)
    
    In [7]: dates
    Out[7]: 
    DatetimeIndex(['2013-01-01', '2013-01-02', '2013-01-03', '2013-01-04',
                   '2013-01-05', '2013-01-06'],
                  dtype='datetime64[ns]', freq='D')
    
    In [8]: df = pd.DataFrame(np.random.randn(6,4), index=dates, columns=list('ABCD'))    //np.random.randn(6,4)返回一个样本，具有标准正态分布
    
    In [9]: df
    Out[9]:          // 指定dates为行键，columns为列键
                       A         B         C         D
    2013-01-01  0.469112 -0.282863 -1.509059 -1.135632
    2013-01-02  1.212112 -0.173215  0.119209 -1.044236
    2013-01-03 -0.861849 -2.104569 -0.494929  1.071804
    2013-01-04  0.721555 -0.706771 -1.039575  0.271860
    2013-01-05 -0.424972  0.567020  0.276232 -1.087401
    2013-01-06 -0.673690  0.113648 -1.478427  0.524988
    
    
    In [12]: df2.dtypes    //查看列数据类型
    Out[12]: 
    A           float64
    B    datetime64[ns]
    C           float32
    D             int32
    E          category
    F            object
    dtype: object

## **三、查看数据** ##

**查看头尾数据：**

In [14]: df.head()    //默认值5
    Out[14]: 
                       A         B         C         D
    2013-01-01  0.469112 -0.282863 -1.509059 -1.135632
    2013-01-02  1.212112 -0.173215  0.119209 -1.044236
    2013-01-03 -0.861849 -2.104569 -0.494929  1.071804
    2013-01-04  0.721555 -0.706771 -1.039575  0.271860
    2013-01-05 -0.424972  0.567020  0.276232 -1.087401
    
    In [15]: df.tail(3)     //默认值5
    Out[15]:  
                       A         B         C         D
    2013-01-04  0.721555 -0.706771 -1.039575  0.271860
    2013-01-05 -0.424972  0.567020  0.276232 -1.087401
    2013-01-06 -0.673690  0.113648 -1.478427  0.524988

**查看行键、列键、数据：**

In [16]: df.index
    Out[16]: 
    DatetimeIndex(['2013-01-01', '2013-01-02', '2013-01-03', '2013-01-04',
                   '2013-01-05', '2013-01-06'],
                  dtype='datetime64[ns]', freq='D')
    
    In [17]: df.columns
    Out[17]: Index([u'A', u'B', u'C', u'D'], dtype='object')
    
    In [18]: df.values
    Out[18]: 
    array([[ 0.4691, -0.2829, -1.5091, -1.1356],
           [ 1.2121, -0.1732,  0.1192, -1.0442],
           [-0.8618, -2.1046, -0.4949,  1.0718],
           [ 0.7216, -0.7068, -1.0396,  0.2719],
           [-0.425 ,  0.567 ,  0.2762, -1.0874],
           [-0.6737,  0.1136, -1.4784,  0.525 ]])

**查看数据整体概况，和、平均值、最大、最小等：**

In [19]: df.describe()
    Out[19]: 
                  A         B         C         D
    count  6.000000  6.000000  6.000000  6.000000
    mean   0.073711 -0.431125 -0.687758 -0.233103
    std    0.843157  0.922818  0.779887  0.973118
    min   -0.861849 -2.104569 -1.509059 -1.135632
    25%   -0.611510 -0.600794 -1.368714 -1.076610
    50%    0.022070 -0.228039 -0.767252 -0.386188
    75%    0.658444  0.041933 -0.034326  0.461706
    max    1.212112  0.567020  0.276232  1.071804

train_df.info()
    print('_'*40)
    <class 'pandas.core.frame.DataFrame'>
    RangeIndex: 891 entries, 0 to 890
    Data columns (total 12 columns):
    PassengerId    891 non-null int64
    Survived       891 non-null int64
    Pclass 891 non-null int64
    Name           891 non-null object
    Sex            891 non-null object
    Age            714 non-null float64
    SibSp          891 non-null int64
    Parch          891 non-null int64
    Ticket         891 non-null object
    Fare           891 non-null float64
    Cabin          204 non-null object
    Embarked       889 non-null object
    dtypes: float64(2), int64(5), object(5)
    memory usage: 83.6+ KB
    ________________________________________

train_df.describe(include=['O'])
    
    Name    Sex Ticket  Cabin   Embarked
    count   891 891 891 204 889
    unique  891 2   681 147 3
    top Chronopoulos, Mr. Apostolos male    CA. 2343    G6  S
    freq    1   577 7   4   644

**行或列平均值：**

In [61]: df.mean()
    Out[61]: 
    A   -0.004474
    B   -0.383981
    C   -0.687758
    D    5.000000
    F    3.000000
    dtype: float64

In [62]: df.mean(1)
    Out[62]: 
    2013-01-01    0.872735
    2013-01-02    1.431621
    2013-01-03    0.707731
    2013-01-04    1.395042
    2013-01-05    1.883656
    2013-01-06    1.592306
    Freq: D, dtype: float64

**转置：**

In [20]: df.T
    Out[20]: 
       2013-01-01  2013-01-02  2013-01-03  2013-01-04  2013-01-05  2013-01-06
    A    0.469112    1.212112   -0.861849    0.721555   -0.424972   -0.673690
    B   -0.282863   -0.173215   -2.104569   -0.706771    0.567020    0.113648
    C   -1.509059    0.119209   -0.494929   -1.039575    0.276232   -1.478427
    D   -1.135632   -1.044236    1.071804    0.271860   -1.087401    0.524988

**根据行、列排序：**

In [21]: df.sort_index(axis=1, ascending=False)    //根据轴，可以.sort_index(axis=0, by=None, ascending=True)。by参数只能对列
    Out[21]: 
                       D         C         B         A
    2013-01-01 -1.135632 -1.509059 -0.282863  0.469112
    2013-01-02 -1.044236  0.119209 -0.173215  1.212112
    2013-01-03  1.071804 -0.494929 -2.104569 -0.861849
    2013-01-04  0.271860 -1.039575 -0.706771  0.721555
    2013-01-05 -1.087401  0.276232  0.567020 -0.424972
    2013-01-06  0.524988 -1.478427  0.113648 -0.673690
    Sorting by values
    
    In [22]: df.sort_values(by='B')       //根据值
    Out[22]: 
                       A         B         C         D
    2013-01-03 -0.861849 -2.104569 -0.494929  1.071804
    2013-01-04  0.721555 -0.706771 -1.039575  0.271860
    2013-01-01  0.469112 -0.282863 -1.509059 -1.135632
    2013-01-02  1.212112 -0.173215  0.119209 -1.044236
    2013-01-06 -0.673690  0.113648 -1.478427  0.524988
    2013-01-05 -0.424972  0.567020  0.276232 -1.087401

## **四、选择数据** ##

**选择单列：**

In [23]: df['A']  //可使用df.A
    Out[23]: 
    2013-01-01    0.469112
    2013-01-02    1.212112
    2013-01-03   -0.861849
    2013-01-04    0.721555
    2013-01-05   -0.424972
    2013-01-06   -0.673690
    Freq: D, Name: A, dtype: float64

**选择局部：**

In [24]: df[0:3]
    Out[24]: 
                       A         B         C         D
    2013-01-01  0.469112 -0.282863 -1.509059 -1.135632
    2013-01-02  1.212112 -0.173215  0.119209 -1.044236
    2013-01-03 -0.861849 -2.104569 -0.494929  1.071804
    
    In [25]: df['20130102':'20130104']
    Out[25]: 
                       A         B         C         D
    2013-01-02  1.212112 -0.173215  0.119209 -1.044236
    2013-01-03 -0.861849 -2.104569 -0.494929  1.071804
    2013-01-04  0.721555 -0.706771 -1.039575  0.271860

**标签选择：**  
通过行键，列键

In [26]: df.loc[dates[0]]        //选择一行，会降维
    Out[26]: 
    A    0.469112
    B   -0.282863
    C   -1.509059
    D   -1.135632
    Name: 2013-01-01 00:00:00, dtype: float64

In [27]: df.loc[:,['A','B']]  //局部选择
    Out[27]: 
                       A         B
    2013-01-01  0.469112 -0.282863
    2013-01-02  1.212112 -0.173215
    2013-01-03 -0.861849 -2.104569
    2013-01-04  0.721555 -0.706771
    2013-01-05 -0.424972  0.567020
    2013-01-06 -0.673690  0.113648

In [28]: df.loc['20130102':'20130104',['A','B']]    //局部选择
    Out[28]: 
                       A         B
    2013-01-02  1.212112 -0.173215
    2013-01-03 -0.861849 -2.104569
    2013-01-04  0.721555 -0.706771

In [29]: df.loc['20130102',['A','B']]   //选择一行，会降维
    Out[29]: 
    A    1.212112
    B   -0.173215
    Name: 2013-01-02 00:00:00, dtype: float64

In [30]: df.loc[dates[0],'A']   //选择具体某个元素，会降维
    Out[30]: 0.46911229990718628

In [31]: df.at[dates[0],'A']     //选择具体某个元素，会降维
    Out[31]: 0.46911229990718628

**位置选择：**  
存在一个从0开始类似于数组

In [32]: df.iloc[3]
    Out[32]: 
    A    0.721555
    B   -0.706771
    C   -1.039575
    D    0.271860
    Name: 2013-01-04 00:00:00, dtype: float64

In [33]: df.iloc[3:5,0:2]
    Out[33]: 
                       A         B
    2013-01-04  0.721555 -0.706771
    2013-01-05 -0.424972  0.567020

In [34]: df.iloc[[1,2,4],[0,2]]
    Out[34]: 
                       A         C
    2013-01-02  1.212112  0.119209
    2013-01-03 -0.861849 -0.494929
    2013-01-05 -0.424972  0.276232

In [35]: df.iloc[1:3,:]
    Out[35]: 
                       A         B         C         D
    2013-01-02  1.212112 -0.173215  0.119209 -1.044236
    2013-01-03 -0.861849 -2.104569 -0.494929  1.071804

In [36]: df.iloc[:,1:3]
    Out[36]: 
                       B         C
    2013-01-01 -0.282863 -1.509059
    2013-01-02 -0.173215  0.119209
    2013-01-03 -2.104569 -0.494929
    2013-01-04 -0.706771 -1.039575
    2013-01-05  0.567020  0.276232
    2013-01-06  0.113648 -1.478427

In [37]: df.iloc[1,1]
    Out[37]: -0.17321464905330858

In [38]: df.iat[1,1]
    Out[38]: -0.17321464905330858

**布尔索引：**

In [39]: df[df.A > 0]
    Out[39]: 
                       A         B         C         D
    2013-01-01  0.469112 -0.282863 -1.509059 -1.135632
    2013-01-02  1.212112 -0.173215  0.119209 -1.044236
    2013-01-04  0.721555 -0.706771 -1.039575  0.271860

In [40]: df[df > 0]
    Out[40]: 
                       A         B         C         D
    2013-01-01  0.469112       NaN       NaN       NaN
    2013-01-02  1.212112       NaN  0.119209       NaN
    2013-01-03       NaN       NaN       NaN  1.071804
    2013-01-04  0.721555       NaN       NaN  0.271860
    2013-01-05       NaN  0.567020  0.276232       NaN
    2013-01-06       NaN  0.113648       NaN  0.524988

In [41]: df2 = df.copy()
    
    In [42]: df2['E'] = ['one', 'one','two','three','four','three']
    
    In [43]: df2
    Out[43]: 
                       A         B         C         D      E
    2013-01-01  0.469112 -0.282863 -1.509059 -1.135632    one
    2013-01-02  1.212112 -0.173215  0.119209 -1.044236    one
    2013-01-03 -0.861849 -2.104569 -0.494929  1.071804    two
    2013-01-04  0.721555 -0.706771 -1.039575  0.271860  three
    2013-01-05 -0.424972  0.567020  0.276232 -1.087401   four
    2013-01-06 -0.673690  0.113648 -1.478427  0.524988  three
    
    In [44]: df2[df2['E'].isin(['two','four'])]
    Out[44]: 
                       A         B         C         D     E
    2013-01-03 -0.861849 -2.104569 -0.494929  1.071804   two
    2013-01-05 -0.424972  0.567020  0.276232 -1.087401  four

## **五、修改数据** ##

**读取时将多列并成一列：**

def parse(x):
        return datetime.strptime(x, '%Y %m %d %H')
    dataset = read_csv('raw.csv',  parse_dates = [['year', 'month', 'day', 'hour']], index_col=0, date_parser=parse)

**Series赋值列：**

In [45]: s1 = pd.Series([1,2,3,4,5,6], index=pd.date_range('20130102', periods=6))
    
    In [46]: s1
    Out[46]: 
    2013-01-02    1
    2013-01-03    2
    2013-01-04    3
    2013-01-05    4
    2013-01-06    5
    2013-01-07    6
    Freq: D, dtype: int64
    
    In [47]: df['F'] = s1     //通过Series赋值列

**赋值单个元素：**

df.at[dates[0],'A'] = 0
    df.iat[0,1] = 0

df.loc[:,'D'] = np.array([5] * len(df))   //通过numpy赋值列
    In [51]: df
    Out[51]: 
                       A         B         C  D    F
    2013-01-01  0.000000  0.000000 -1.509059  5  NaN
    2013-01-02  1.212112 -0.173215  0.119209  5  1.0
    2013-01-03 -0.861849 -2.104569 -0.494929  5  2.0
    2013-01-04  0.721555 -0.706771 -1.039575  5  3.0
    2013-01-05 -0.424972  0.567020  0.276232  5  4.0
    2013-01-06 -0.673690  0.113648 -1.478427  5  5.0

In [52]: df2 = df.copy()
    
    In [53]: df2[df2 > 0] = -df2    //为每个数据赋值
    
    In [54]: df2
    Out[54]: 
                       A         B         C  D    F
    2013-01-01  0.000000  0.000000 -1.509059 -5  NaN
    2013-01-02 -1.212112 -0.173215 -0.119209 -5 -1.0
    2013-01-03 -0.861849 -2.104569 -0.494929 -5 -2.0
    2013-01-04 -0.721555 -0.706771 -1.039575 -5 -3.0
    2013-01-05 -0.424972 -0.567020 -0.276232 -5 -4.0
    2013-01-06 -0.673690 -0.113648 -1.478427 -5 -5.0

**修改索引：**

In [55]: df1 = df.reindex(index=dates[0:4], columns=list(df.columns) + ['E'])   //修改DataFrame的键
    
    In [56]: df1.loc[dates[0]:dates[1],'E'] = 1
    
    In [57]: df1
    Out[57]: 
                       A         B         C  D    F    E
    2013-01-01  0.000000  0.000000 -1.509059  5  NaN  1.0
    2013-01-02  1.212112 -0.173215  0.119209  5  1.0  1.0
    2013-01-03 -0.861849 -2.104569 -0.494929  5  2.0  NaN
    2013-01-04  0.721555 -0.706771 -1.039575  5  3.0  NaN

## **六、缺失值处理** ##

pandas用numpy.nan表示缺失值，不参与计算。  
**去掉缺失行：**

In [58]: df1.dropna(how='any')
    Out[58]: 
                       A         B         C  D    F    E
    2013-01-02  1.212112 -0.173215  0.119209  5  1.0  1.0

**填充缺失值：**

In [59]: df1.fillna(value=5)   //对缺失值处进行填充
    Out[59]: 
                       A         B         C  D    F    E
    2013-01-01  0.000000  0.000000 -1.509059  5  5.0  1.0
    2013-01-02  1.212112 -0.173215  0.119209  5  1.0  1.0
    2013-01-03 -0.861849 -2.104569 -0.494929  5  2.0  5.0
    2013-01-04  0.721555 -0.706771 -1.039575  5  3.0  5.0

**判断何处缺失：**

In [60]: pd.isnull(df1)    //判断位置元素是否为缺失值
    Out[60]: 
                    A      B      C      D      F      E
    2013-01-01  False  False  False  False   True  False
    2013-01-02  False  False  False  False  False  False
    2013-01-03  False  False  False  False  False   True
    2013-01-04  False  False  False  False  False   True

## **七、操作** ##

**偏移（对齐）元素：**

In [63]: s = pd.Series([1,3,5,np.nan,6,8], index=dates).shift(2)                   //序列元素偏移两位
    
    In [64]: s
    Out[64]: 
    2013-01-01    NaN
    2013-01-02    NaN
    2013-01-03    1.0
    2013-01-04    3.0
    2013-01-05    5.0
    2013-01-06    NaN
    Freq: D, dtype: float64
    
    In [65]: df.sub(s, axis='index')
    Out[65]: 
                       A         B         C    D    F
    2013-01-01       NaN       NaN       NaN  NaN  NaN
    2013-01-02       NaN       NaN       NaN  NaN  NaN
    2013-01-03 -1.861849 -3.104569 -1.494929  4.0  1.0
    2013-01-04 -2.278445 -3.706771 -4.039575  2.0  0.0
    2013-01-05 -5.424972 -4.432980 -4.723768  0.0 -1.0
    2013-01-06       NaN       NaN       NaN  NaN  NaN

**对元素应用函数：**

In [66]: df.apply(np.cumsum)    //对对象每个元素应用函数
    Out[66]: 
                       A         B         C   D     F
    2013-01-01  0.000000  0.000000 -1.509059   5   NaN
    2013-01-02  1.212112 -0.173215 -1.389850  10   1.0
    2013-01-03  0.350263 -2.277784 -1.884779  15   3.0
    2013-01-04  1.071818 -2.984555 -2.924354  20   6.0
    2013-01-05  0.646846 -2.417535 -2.648122  25  10.0
    2013-01-06 -0.026844 -2.303886 -4.126549  30  15.0
    
    In [67]: df.apply(lambda x: x.max() - x.min())
    Out[67]: 
    A    2.073961
    B    2.671590
    C    1.785291
    D    0.000000
    F    4.000000
    dtype: float64

**直方图：**

In [68]: s = pd.Series(np.random.randint(0, 7, size=10))
    
    In [69]: s
    Out[69]: 
    0    4
    1    2
    2    1
    3    2
    4    6
    5    4
    6    4
    7    6
    8    4
    9    4
    dtype: int64
    
    In [70]: s.value_counts()   //统计值以数字格式显示直方图
    Out[70]: 
    4    5
    6    2
    2    2
    1    1
    dtype: int64

**字符串操作：**

In [71]: s = pd.Series(['A', 'B', 'C', 'Aaba', 'Baca', np.nan, 'CABA', 'dog', 'cat'])
    
    In [72]: s.str.lower()   //序列字符串转成小写字母
    Out[72]: 
    0       a
    1       b
    2       c
    3    aaba
    4    baca
    5     NaN
    6    caba
    7     dog
    8     cat
    dtype: object

## **八、合并** ##

**Comcat：**

In [73]: df = pd.DataFrame(np.random.randn(10, 4))
    
    In [74]: df
    Out[74]: 
              0         1         2         3
    0 -0.548702  1.467327 -1.015962 -0.483075
    1  1.637550 -1.217659 -0.291519 -1.745505
    2 -0.263952  0.991460 -0.919069  0.266046
    3 -0.709661  1.669052  1.037882 -1.705775
    4 -0.919854 -0.042379  1.247642 -0.009920
    5  0.290213  0.495767  0.362949  1.548106
    6 -1.131345 -0.089329  0.337863 -0.945867
    7 -0.932132  1.956030  0.017587 -0.016692
    8 -0.575247  0.254161 -1.143704  0.215897
    9  1.193555 -0.077118 -0.408530 -0.862495
    
    # break it into pieces
    In [75]: pieces = [df[:3], df[3:7], df[7:]]
    
    In [76]: pd.concat(pieces)
    Out[76]: 
              0         1         2         3
    0 -0.548702  1.467327 -1.015962 -0.483075
    1  1.637550 -1.217659 -0.291519 -1.745505
    2 -0.263952  0.991460 -0.919069  0.266046
    3 -0.709661  1.669052  1.037882 -1.705775
    4 -0.919854 -0.042379  1.247642 -0.009920
    5  0.290213  0.495767  0.362949  1.548106
    6 -1.131345 -0.089329  0.337863 -0.945867
    7 -0.932132  1.956030  0.017587 -0.016692
    8 -0.575247  0.254161 -1.143704  0.215897
    9  1.193555 -0.077118 -0.408530 -0.862495

**Join：**

In [78]: right = pd.DataFrame({
       'key': ['foo', 'foo'], 'rval': [4, 5]})
    
    In [79]: left
    Out[79]: 
       key  lval
    0  foo     1
    1  foo     2
    
    In [80]: right
    Out[80]: 
       key  rval
    0  foo     4
    1  foo     5
    
    In [81]: pd.merge(left, right, on='key')
    Out[81]: 
       key  lval  rval
    0  foo     1     4
    1  foo     1     5
    2  foo     2     4
    3  foo     2     5

In [82]: left = pd.DataFrame({
       'key': ['foo', 'bar'], 'lval': [1, 2]})
    
    In [83]: right = pd.DataFrame({
       'key': ['foo', 'bar'], 'rval': [4, 5]})
    
    In [84]: left
    Out[84]: 
       key  lval
    0  foo     1
    1  bar     2
    
    In [85]: right
    Out[85]: 
       key  rval
    0  foo     4
    1  bar     5
    
    In [86]: pd.merge(left, right, on='key')
    Out[86]: 
       key  lval  rval
    0  foo     1     4
    1  bar     2     5

**Append：**

In [87]: df = pd.DataFrame(np.random.randn(8, 4), columns=['A','B','C','D'])
    
    In [88]: df
    Out[88]: 
              A         B         C         D
    0  1.346061  1.511763  1.627081 -0.990582
    1 -0.441652  1.211526  0.268520  0.024580
    2 -1.577585  0.396823 -0.105381 -0.532532
    3  1.453749  1.208843 -0.080952 -0.264610
    4 -0.727965 -0.589346  0.339969 -0.693205
    5 -0.339355  0.593616  0.884345  1.591431
    6  0.141809  0.220390  0.435589  0.192451
    7 -0.096701  0.803351  1.715071 -0.708758
    
    In [89]: s = df.iloc[3]
    
    In [90]: df.append(s, ignore_index=True)
    Out[90]: 
              A         B         C         D
    0  1.346061  1.511763  1.627081 -0.990582
    1 -0.441652  1.211526  0.268520  0.024580
    2 -1.577585  0.396823 -0.105381 -0.532532
    3  1.453749  1.208843 -0.080952 -0.264610
    4 -0.727965 -0.589346  0.339969 -0.693205
    5 -0.339355  0.593616  0.884345  1.591431
    6  0.141809  0.220390  0.435589  0.192451
    7 -0.096701  0.803351  1.715071 -0.708758
    8  1.453749  1.208843 -0.080952 -0.264610

## **九、分组** ##

In [91]: df = pd.DataFrame({
       'A' : ['foo', 'bar', 'foo', 'bar',
       ....:                           'foo', 'bar', 'foo', 'foo'],
       ....:                    'B' : ['one', 'one', 'two', 'three',
       ....:                           'two', 'two', 'one', 'three'],
       ....:                    'C' : np.random.randn(8),
       ....:                    'D' : np.random.randn(8)})
       ....: 
    
    In [92]: df
    Out[92]: 
         A      B         C         D
    0  foo    one -1.202872 -0.055224
    1  bar    one -1.814470  2.395985
    2  foo    two  1.018601  1.552825
    3  bar  three -0.595447  0.166599
    4  foo    two  1.395433  0.047609
    5  bar    two -0.392670 -0.136473
    6  foo    one  0.007207 -0.561757
    7  foo  three  1.928123 -1.623033
    
    In [93]: df.groupby('A').sum() //对键index A分组进行并对每个组执行sum函数
    Out[93]: 
                C        D
    A                     
    bar -2.802588  2.42611
    foo  3.146492 -0.63958

In [94]: df.groupby(['A','B']).sum()  //对index A B进行分组并对每个组执行sum函数
    Out[94]: 
                      C         D
    A   B                        
    bar one   -1.814470  2.395985
        three -0.595447  0.166599
        two   -0.392670 -0.136473
    foo one   -1.195665 -0.616981
        three  1.928123 -1.623033
        two    2.414034  1.600434

## **十、重切片** ##

**stack：**压缩DataFrame列

In [99]: df2
    Out[99]: 
                         A         B
    first second                    
    bar   one     0.029399 -0.542108
          two     0.282696 -0.087302
    baz   one    -1.575170  1.771208
          two     0.816482  1.100230
    In [100]: stacked = df2.stack()
    
    In [101]: stacked  = df2.stack()
    Out[101]: stacked
    first  second   
    bar    one     A    0.029399
                   B   -0.542108
           two     A    0.282696
                   B   -0.087302
    baz    one     A   -1.575170
                   B    1.771208
           two     A    0.816482
                   B    1.100230
    dtype: float64

**unstack**反解压到上一层，不同参数解压层不同

In [102]: stacked.unstack()
    Out[102]: 
                         A         B
    first second                    
    bar   one     0.029399 -0.542108
          two     0.282696 -0.087302
    baz   one    -1.575170  1.771208
          two     0.816482  1.100230
    
    In [103]: stacked.unstack(1)
    Out[103]: 
    second        one       two
    first                      
    bar   A  0.029399  0.282696
          B -0.542108 -0.087302
    baz   A -1.575170  0.816482
          B  1.771208  1.100230
    
    In [104]: stacked.unstack(0)
    Out[104]: 
    first          bar       baz
    second                      
    one    A  0.029399 -1.575170
           B -0.542108  1.771208
    two    A  0.282696  0.816482

**透视Pivot表：**

In [106]: df
    Out[106]: 
            A  B    C         D         E
    0     one  A  foo  1.418757 -0.179666
    1     one  B  foo -1.879024  1.291836
    2     two  C  foo  0.536826 -0.009614
    3   three  A  bar  1.006160  0.392149
    4     one  B  bar -0.029716  0.264599
    5     one  C  bar -1.146178 -0.057409
    6     two  A  foo  0.100900 -1.425638
    7   three  B  foo -1.035018  1.024098
    8     one  C  foo  0.314665 -0.106062
    9     one  A  bar -0.773723  1.824375
    10    two  B  bar -1.170653  0.595974
    11  three  C  bar  0.648740  1.167115
    In [107]: pd.pivot_table(df, values='D', index=['A', 'B'], columns=['C'])
    Out[107]: 
    C             bar       foo
    A     B                    
    one   A -0.773723  1.418757
          B -0.029716 -1.879024
          C -1.146178  0.314665
    three A  1.006160       NaN
          B       NaN -1.035018
          C  0.648740       NaN
    two   A       NaN  0.100900
          B -1.170653       NaN
          C       NaN  0.536826

## **十一、时间序列** ##

**生成：**

In [108]: rng = pd.date_range('1/1/2012', periods=100, freq='S')
    
    In [109]: ts = pd.Series(np.random.randint(0, 500, len(rng)), index=rng)
    
    In [110]: ts.resample('5Min').sum()
    Out[110]: 
    2012-01-01    25083
    Freq: 5T, dtype: int64

In [111]: rng = pd.date_range('3/6/2012 00:00', periods=5, freq='D')
    
    In [112]: ts = pd.Series(np.random.randn(len(rng)), rng)
    
    In [113]: ts
    Out[113]: 
    2012-03-06    0.464000
    2012-03-07    0.227371
    2012-03-08   -0.496922
    2012-03-09    0.306389
    2012-03-10   -2.290613
    Freq: D, dtype: float64
    
    In [114]: ts_utc = ts.tz_localize('UTC')
    
    In [115]: ts_utc
    Out[115]: 
    2012-03-06 00:00:00+00:00    0.464000
    2012-03-07 00:00:00+00:00    0.227371
    2012-03-08 00:00:00+00:00   -0.496922
    2012-03-09 00:00:00+00:00    0.306389
    2012-03-10 00:00:00+00:00   -2.290613
    Freq: D, dtype: float64

**转换时间区：**

In [116]: ts_utc.tz_convert('US/Eastern')
    Out[116]: 
    2012-03-05 19:00:00-05:00    0.464000
    2012-03-06 19:00:00-05:00    0.227371
    2012-03-07 19:00:00-05:00   -0.496922
    2012-03-08 19:00:00-05:00    0.306389
    2012-03-09 19:00:00-05:00   -2.290613
    Freq: D, dtype: float64

**显示格式转换：**

In [117]: rng = pd.date_range('1/1/2012', periods=5, freq='M')
    
    In [118]: ts = pd.Series(np.random.randn(len(rng)), index=rng)
    
    In [119]: ts
    Out[119]: 
    2012-01-31   -1.134623
    2012-02-29   -1.561819
    2012-03-31   -0.260838
    2012-04-30    0.281957
    2012-05-31    1.523962
    Freq: M, dtype: float64
    
    In [120]: ps = ts.to_period()
    
    In [121]: ps
    Out[121]: 
    2012-01   -1.134623
    2012-02   -1.561819
    2012-03   -0.260838
    2012-04    0.281957
    2012-05    1.523962
    Freq: M, dtype: float64
    
    In [122]: ps.to_timestamp()
    Out[122]: 
    2012-01-01   -1.134623
    2012-02-01   -1.561819
    2012-03-01   -0.260838
    2012-04-01    0.281957
    2012-05-01    1.523962
    Freq: MS, dtype: float64

In [123]: prng = pd.period_range('1990Q1', '2000Q4', freq='Q-NOV')
    
    In [124]: ts = pd.Series(np.random.randn(len(prng)), prng)
    
    In [125]: ts.index = (prng.asfreq('M', 'e') + 1).asfreq('H', 's') + 9
    
    In [126]: ts.head()
    Out[126]: 
    1990-03-01 09:00   -0.902937
    1990-06-01 09:00    0.068159
    1990-09-01 09:00   -0.057873
    1990-12-01 09:00   -0.368204
    1991-03-01 09:00   -1.144073
    Freq: H, dtype: float64

## **十二、categoricals** ##

version 0.15后DataFrame能够包含categorical

In [127]: df = pd.DataFrame({
       "id":[1,2,3,4,5,6], "raw_grade":['a', 'b', 'b', 'a', 'a', 'e']})
    In [128]: df["grade"] = df["raw_grade"].astype("category")
    
    In [129]: df["grade"]
    Out[129]: 
    0    a
    1    b
    2    b
    3    a
    4    a
    5    e
    Name: grade, dtype: category
    Categories (3, object): [a, b, e]

**重命名categorical：**

df["grade"].cat.categories = ["very good", "good", "very bad"]

**重排categorical并加入缺失categorical：**

In [131]: df["grade"] = df["grade"].cat.set_categories(["very bad", "bad", "medium", "good", "very good"])
    
    In [132]: df["grade"]
    Out[132]: 
    0    very good
    1         good
    2         good
    3    very good
    4    very good
    5     very bad
    Name: grade, dtype: category
    Categories (5, object): [very bad, bad, medium, good, very good]

**根据categorical排序：**

In [133]: df.sort_values(by="grade")
    Out[133]: 
       id raw_grade      grade
    5   6         e   very bad
    1   2         b       good
    2   3         b       good
    0   1         a  very good
    3   4         a  very good

**分组categorical：**

In [134]: df.groupby("grade").size()
    Out[134]: 
    grade
    very bad     1
    bad          0
    medium       0
    good         2
    very good    3
    dtype: int64

## **十三、画图** ##

[官方文档][Link 2]  
一般不使用pandas的画图功能，而使用其他如matplotlib等。

## **十四、读取存储** ##

**CSV：**

写入：
     df.to_csv('foo.csv')
    读取：
     In [142]: pd.read_csv('foo.csv')
    Out[142]: 
         Unnamed: 0          A          B         C          D
    0    2000-01-01   0.266457  -0.399641 -0.219582   1.186860
    1    2000-01-02  -1.170732  -0.345873  1.653061  -0.282953
    2    2000-01-03  -1.734933   0.530468  2.060811  -0.515536
    3    2000-01-04  -1.555121   1.452620  0.239859  -1.156896
    4    2000-01-05   0.578117   0.511371  0.103552  -2.428202
    5    2000-01-06   0.478344   0.449933 -0.741620  -1.962409
    6    2000-01-07   1.235339  -0.091757 -1.543861  -1.084753
    ..          ...        ...        ...       ...        ...
    993  2002-09-20 -10.628548  -9.153563 -7.883146  28.313940
    994  2002-09-21 -10.390377  -8.727491 -6.399645  30.914107
    995  2002-09-22  -8.985362  -8.485624 -4.669462  31.367740
    996  2002-09-23  -9.558560  -8.781216 -4.499815  30.518439
    997  2002-09-24  -9.902058  -9.340490 -4.386639  30.105593
    998  2002-09-25 -10.216020  -9.480682 -3.933802  29.758560
    999  2002-09-26 -11.856774 -10.671012 -3.216025  29.369368
    
    [1000 rows x 5 columns]

**HDF5：**

df.to_hdf('foo.h5','df')
    In [144]: pd.read_hdf('foo.h5','df')
    Out[144]: 
                        A          B         C          D
    2000-01-01   0.266457  -0.399641 -0.219582   1.186860
    2000-01-02  -1.170732  -0.345873  1.653061  -0.282953
    2000-01-03  -1.734933   0.530468  2.060811  -0.515536
    2000-01-04  -1.555121   1.452620  0.239859  -1.156896
    2000-01-05   0.578117   0.511371  0.103552  -2.428202
    2000-01-06   0.478344   0.449933 -0.741620  -1.962409
    2000-01-07   1.235339  -0.091757 -1.543861  -1.084753
    ...               ...        ...       ...        ...
    2002-09-20 -10.628548  -9.153563 -7.883146  28.313940
    2002-09-21 -10.390377  -8.727491 -6.399645  30.914107
    2002-09-22  -8.985362  -8.485624 -4.669462  31.367740
    2002-09-23  -9.558560  -8.781216 -4.499815  30.518439
    2002-09-24  -9.902058  -9.340490 -4.386639  30.105593
    2002-09-25 -10.216020  -9.480682 -3.933802  29.758560
    2002-09-26 -11.856774 -10.671012 -3.216025  29.369368
    
    [1000 rows x 4 columns]

**EXCEL：**

df.to_excel('foo.xlsx', sheet_name='Sheet1')
    In [146]: pd.read_excel('foo.xlsx', 'Sheet1', index_col=None, na_values=['NA'])
    Out[146]: 
                        A          B         C          D
    2000-01-01   0.266457  -0.399641 -0.219582   1.186860
    2000-01-02  -1.170732  -0.345873  1.653061  -0.282953
    2000-01-03  -1.734933   0.530468  2.060811  -0.515536
    2000-01-04  -1.555121   1.452620  0.239859  -1.156896
    2000-01-05   0.578117   0.511371  0.103552  -2.428202
    2000-01-06   0.478344   0.449933 -0.741620  -1.962409
    2000-01-07   1.235339  -0.091757 -1.543861  -1.084753
    ...               ...        ...       ...        ...
    2002-09-20 -10.628548  -9.153563 -7.883146  28.313940
    2002-09-21 -10.390377  -8.727491 -6.399645  30.914107
    2002-09-22  -8.985362  -8.485624 -4.669462  31.367740
    2002-09-23  -9.558560  -8.781216 -4.499815  30.518439
    2002-09-24  -9.902058  -9.340490 -4.386639  30.105593
    2002-09-25 -10.216020  -9.480682 -3.933802  29.758560
    2002-09-26 -11.856774 -10.671012 -3.216025  29.369368
    
    [1000 rows x 4 columns]

[Link 1]: http://pandas.pydata.org/pandas-docs/stable/10min.html#
[matplotlib]: http://matplotlib.org/gallery.html
[pandas]: http://pandas.pydata.org/pandas-docs/stable/tutorials.html
[Link 2]: http://pandas.pydata.org/pandas-docs/stable/visualization.html#visualization