Python数据处理——Pandas模块使用（四）

深碍√TFBOYSˉ_ 2022-05-23 03:50 244阅读 0赞

### 本文主要介绍pandas数据清洗和数据操作 ###

##### 1. 数据统计 #####

In [31]: df = DataFrame({
       'A':np.random.randn(5),'B':np.random.randn(5)})
    
    In [32]: df
    Out[32]:
              A         B
    0 -0.635732  0.738902
    1 -1.100320  0.910203
    2  1.503987 -2.030411
    3  0.548760  0.228552
    4 -2.201917  1.676173
    
    In [33]: df.count()    #计算个数
    Out[33]:
    A    5
    B    5
    dtype: int64
    In [34]: df.min()   #最小值
    Out[34]:
    A   -2.201917
    B   -2.030411
    dtype: float64
    In [35]: df.max()   #最大值
    Out[35]:
    A    1.503987
    B    1.676173
    dtype: float64
    In [36]: df.idxmin()  #最小值的位置
    Out[36]:
    A    4
    B    2
    dtype: int64
    In [37]: df.idxmax()   #最大值的位置
    Out[37]:
    A    2
    B    4
    dtype: int64
    In [38]: df.sum()    #求和
    Out[38]:
    A   -1.885221
    B    1.523419
    dtype: float64
    In [39]: df.mean()   #平均数
    Out[39]:
    A   -0.377044
    B    0.304684
    dtype: float64
    In [40]: df.median()   #中位数
    Out[40]:
    A   -0.635732
    B    0.738902
    dtype: float64
    In [41]: df.mode()  #众数
    Out[41]:
    Empty DataFrame
    Columns: [A, B]
    Index: []
    In [42]: df.var()    #方差
    Out[42]:
    A    2.078900
    B    1.973661
    dtype: float64
    In [43]: df.std()    #标准差
    Out[43]:
    A    1.441839
    B    1.404871
    dtype: float64
    In [44]: df.mad()    #平均绝对偏差
    Out[44]:
    A    1.122734
    B    0.964491
    dtype: float64
    In [45]: df.skew()   #偏度
    Out[45]:
    A    0.135719
    B   -1.480080
    dtype: float64
    In [46]: df.kurt()   #峰度
    Out[46]:
    A   -0.878539
    B    2.730675
    dtype: float64
    In [48]: df.quantile(0.25)   #25%分位数
    Out[48]:
    A   -1.100320
    B    0.228552
    dtype: float64
    In [49]: df.describe()    #描述性统计指标
    Out[49]:
                  A         B
    count  5.000000  5.000000
    mean  -0.377044  0.304684
    std    1.441839  1.404871
    min   -2.201917 -2.030411
    25%   -1.100320  0.228552
    50%   -0.635732  0.738902
    75%    0.548760  0.910203
    max    1.503987  1.676173

`pandas` 有个非常简便的方法一次得到这些统计分析，那就是`agg()`函数，如：

# 自定义函数
    def first(columns):
        return columns[0]
    
    df.agg(mean,cout,max,first).reset_index()

#### 2. 处理缺失值 ####

In [50]: string = Series(['apple','banana','pear',np.nan,'grape'])
    
    In [51]: string
    Out[51]:
    0     apple
    1    banana
    2      pear
    3       NaN
    4     grape
    dtype: object
    
    In [52]: string.isnull()  #判断是否为缺失值
    Out[52]:
    0    False
    1    False
    2    False
    3     True
    4    False
    dtype: bool
    
    In [53]: string.dropna()  #过滤缺失值，默认过滤任何含NaN的行
    Out[53]:
    0     apple
    1    banana
    2      pear
    4     grape
    dtype: object
    
    In [54]: string.fillna(0)  #填充缺失值
    Out[54]:
    0     apple
    1    banana
    2      pear
    3         0
    4     grape
    dtype: object
    
    In [55]: string.ffill()   #向前填充
    Out[55]:
    0     apple
    1    banana
    2      pear
    3      pear
    4     grape
    dtype: object
    
    In [56]: data = DataFrame([[1. ,6.5,3],[1. ,np.nan,np.nan],[np.nan,np.nan,np.nan],[np.nan,7,9]])  #DataFrame操作同理
    In [57]: data
    Out[57]:
         0    1    2
    0  1.0  6.5  3.0
    1  1.0  NaN  NaN
    2  NaN  NaN  NaN
    3  NaN  7.0  9.0

#### 3. 层次化索引 ####

In [6]:  data = Series(np.random.randn(10),index=[['a','a','a','b','b','b','c','c','d','d'],[1,2,3,1,2,3,1,2,2,3]])
    
    In [7]: data
    Out[7]:
    a  1    0.386697
       2    0.822063
       3    0.338441
    b  1    0.017249
       2    0.880122
       3    0.296465
    c  1    0.376104
       2   -1.309419
    d  2    0.512754
       3    0.223535
    dtype: float64
    
    In [8]: data.index  
    Out[8]:
    MultiIndex(levels=[[u'a', u'b', u'c', u'd'], [1, 2, 3]],
               labels=[[0, 0, 0, 1, 1, 1, 2, 2, 3, 3], [0, 1, 2, 0, 1, 2, 0, 1, 1, 2]])
    
    
    In [10]: data['b':'c']
    Out[10]:
    b  1    0.017249
       2    0.880122
       3    0.296465
    c  1    0.376104
       2   -1.309419
    dtype: float64
    
    In [11]: data[:,2]
    Out[11]:
    a    0.822063
    b    0.880122
    c   -1.309419
    d    0.512754
    dtype: float64
    
    In [12]: data.unstack()
    Out[12]:
              1         2         3
    a  0.386697  0.822063  0.338441
    b  0.017249  0.880122  0.296465
    c  0.376104 -1.309419       NaN
    d       NaN  0.512754  0.223535
    
    In [13]: data.unstack().stack()
    Out[13]:
    a  1    0.386697
       2    0.822063
       3    0.338441
    b  1    0.017249
       2    0.880122
       3    0.296465
    c  1    0.376104
       2   -1.309419
    d  2    0.512754
       3    0.223535
    dtype: float64
    
    In [14]: df = DataFrame(np.arange(12).reshape(4,3),index=[['a','a','b','b'],[1,2,1,2]],columns=[['Ohio','Ohio','Colorad ...: o'],['Green','Red','Green']])
    
    In [15]: df
    Out[15]:
         Ohio     Colorado
        Green Red    Green
    a 1     0   1        2
      2     3   4        5
    b 1     6   7        8
      2     9  10       11
    
    In [16]: df.index.names = ['key1','key2']
    In [17]: df.columns.names = ['state','color']
    
    In [18]: df
    Out[18]:
    state      Ohio     Colorado
    color     Green Red    Green
    key1 key2
    a    1        0   1        2
         2        3   4        5
    b    1        6   7        8
         2        9  10       11
    
    In [19]: df['Ohio']    #降维
    Out[19]:
    color      Green  Red
    key1 key2
    a    1         0    1
         2         3    4
    b    1         6    7
         2         9   10
    
    In [20]: df.swaplevel('key1','key2')
    Out[20]:
    state      Ohio     Colorado
    color     Green Red    Green
    key2 key1
    1    a        0   1        2
    2    a        3   4        5
    1    b        6   7        8
    2    b        9  10       11
    
    In [21]: df.sortlevel(1)    #key2
    Out[21]:
    state      Ohio     Colorado
    color     Green Red    Green
    key1 key2
    a    1        0   1        2
    b    1        6   7        8
    a    2        3   4        5
    b    2        9  10       11
    
    In [22]: df.sortlevel(0)  #key1
    Out[22]:
    state      Ohio     Colorado
    color     Green Red    Green
    key1 key2
    a    1        0   1        2
         2        3   4        5
    b    1        6   7        8
         2        9  10       11

#### 4. 类sql操作 ####

In [5]: dic = {
       'Name':['LiuShunxiang','Zhangshan','ryan'],
       ...: 'Sex':['M','F','F'],
       ...: 'Age':[27,23,24],
       ...: 'Height':[165.7,167.2,154],
       ...: 'Weight':[61,63,41]}
    
    In [6]: student = pd.DataFrame(dic)
    In [7]: student
    Out[7]:
       Age  Height          Name Sex  Weight
    0   27   165.7  LiuShunxiang   M      61
    1   23   167.2     Zhangshan   F      63
    2   24   154.0          ryan   F      41
    
    In [8]: dic1 = {
       'Name':['Ann','Joe'],
       ...: 'Sex':['M','F'],
       ...: 'Age':[27,33],
       ...: 'Height':[168,177.2],
       ...: 'Weight':[51,65]}
    
    In [9]: student1 =  pd.DataFrame(dic1)
    
    In [10]: Student = pd.concat([student,student1])  #插入行
    In [11]: Student
    Out[11]:
       Age  Height          Name Sex  Weight
    0   27   165.7  LiuShunxiang   M      61
    1   23   167.2     Zhangshan   F      63
    2   24   154.0          ryan   F      41
    0   27   168.0           Ann   M      51
    1   33   177.2           Joe   F      65
    
    In [14]:  pd.DataFrame(Student,columns = ['Age','Height','Name','Sex','Weight','Score'])   #新增列
    Out[14]:
       Age  Height          Name Sex  Weight  Score
    0   27   165.7  LiuShunxiang   M      61    NaN
    1   23   167.2     Zhangshan   F      63    NaN
    2   24   154.0          ryan   F      41    NaN
    0   27   168.0           Ann   M      51    NaN
    1   33   177.2           Joe   F      65    NaN
    
    In [16]:  Student.ix[Student['Name']=='ryan','Height'] = 160  #修改某个数据
    In [17]: Student
    Out[17]:
       Age  Height          Name Sex  Weight
    0   27   165.7  LiuShunxiang   M      61
    1   23   167.2     Zhangshan   F      63
    2   24   160.0          ryan   F      41
    0   27   168.0           Ann   M      51
    1   33   177.2           Joe   F      65
    
    In [18]: Student[Student['Height']>160]   #删选
    Out[18]:
       Age  Height          Name Sex  Weight
    0   27   165.7  LiuShunxiang   M      61
    1   23   167.2     Zhangshan   F      63
    0   27   168.0           Ann   M      51
    1   33   177.2           Joe   F      65
    
    In [21]: Student.drop(['Weight'],axis = 1).head() #删除列
    Out[21]:
       Age  Height          Name Sex
    0   27   165.7  LiuShunxiang   M
    1   23   167.2     Zhangshan   F
    2   24   160.0          ryan   F
    0   27   168.0           Ann   M
    1   33   177.2           Joe   F
    
    In [22]: Student.drop([1,2])   #删除行索引为1和2的行
    Out[22]:
       Age  Height          Name Sex  Weight
    0   27   165.7  LiuShunxiang   M      61
    0   27   168.0           Ann   M      51
    
    In [24]: Student.drop(['Age'],axis = 1)   #删除列索引为Age的列
    Out[24]:
       Height          Name Sex  Weight
    0   165.7  LiuShunxiang   M      61
    1   167.2     Zhangshan   F      63
    2   154.0          ryan   F      41
    0   168.0           Ann   M      51
    1   177.2           Joe   F      65
    
    
    In [26]: Student.groupby('Sex').agg([np.mean,np.median])   #等价于SELECT…FROM…GROUP BY…功能
    Out[26]:
               Age             Height             Weight
              mean median        mean  median       mean median
    Sex
    F    26.666667     24  168.133333  167.20  56.333333     63
    M    27.000000     27  166.850000  166.85  56.000000     56
    
    In [27]: series = pd.Series(np.random.randint(1,20,5))    #排序
    In [28]: series
    Out[28]:
    0     9
    1    17
    2    17
    3    13
    4    15
    dtype: int32
    
    In [29]: series.order()   #默认升序
    C:/Anaconda2/Scripts/ipython-script.py:1: FutureWarning: order is deprecated, use sort_values(...)
      if __name__ == '__main__':
    Out[29]:
    0     9
    3    13
    4    15
    1    17
    2    17
    dtype: int32
    
    In [30]: series.order(ascending = False)  #降序
    C:/Anaconda2/Scripts/ipython-script.py:1: FutureWarning: order is deprecated, use sort_values(...)
      if __name__ == '__main__':
    Out[30]:
    2    17
    1    17
    4    15
    3    13
    0     9
    dtype: int32
    
    In [31]: Student.sort_values(by = ['Height'])   #按值排序
    Out[31]:
       Age  Height          Name Sex  Weight
    2   24   160.0          ryan   F      41
    0   27   165.7  LiuShunxiang   M      61
    1   23   167.2     Zhangshan   F      63
    0   27   168.0           Ann   M      51
    1   33   177.2           Joe   F      65
    
    In [32]: dict2 = {
       'Name':['ryan','LiuShunxiang','Zhangshan','Ann','Joe'],   
        ...:          'Score':['89','90','78','60','53']}
    
    In [33]: Score = pd.DataFrame(dict2)
    In [34]: Score
    Out[34]:
               Name Score
    0          ryan    89
    1  LiuShunxiang    90
    2     Zhangshan    78
    3           Ann    60
    4           Joe    53
    
    In [35]: stu_score = pd.merge(Student,Score,on = 'Name')   #表连接
    In [36]: stu_score
    Out[36]:
       Age  Height          Name Sex  Weight Score
    0   27   165.7  LiuShunxiang   M      61    90
    1   23   167.2     Zhangshan   F      63    78
    2   24   160.0          ryan   F      41    89
    3   27   168.0           Ann   M      51    60
    4   33   177.2           Joe   F      65    53

`注：student1以dic形式转DataFrame对象和直接新建DataFrame对象，连接结果不同`

In [71]:student1 =  DataFrame({
       'name';['Ann','Joe'],'Sex':['M','F'],'Age':[27,33],'Height':[168,177.2],'Weight':[51,65
        ...: ]})
    In [72]: student
    Out[72]:
       Age  Height          Name Sex  Weight
    0   27   165.7  LiuShunxiang   M      61
    1   23   167.2     Zhangshan   F      63
    2   24   154.0          ryan   F      41
    
    In [73]: student1
    Out[73]:
       Age  Height Sex  Weight name
    0   27   168.0   M      51  Ann
    1   33   177.2   F      65  Joe
    
    In [74]: Student = pd.concat([student,student1])
    In [75]: Student
    Out[75]:
       Age  Height          Name Sex  Weight name
    0   27   165.7  LiuShunxiang   M      61  NaN
    1   23   167.2     Zhangshan   F      63  NaN
    2   24   154.0          ryan   F      41  NaN
    0   27   168.0           NaN   M      51  Ann
    1   33   177.2           NaN   F      65  Joe

**延伸表连接，merge函数参数说明如下：**

<table> 
 <thead> 
  <tr> 
   <th align="left">参数</th> 
   <th align="left">说明</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td align="left">left</td> 
   <td align="left">参与合并的左侧DataFrame</td> 
  </tr> 
  <tr> 
   <td align="left">right</td> 
   <td align="left">参与合并的右侧DataFrame</td> 
  </tr> 
  <tr> 
   <td align="left">how</td> 
   <td align="left">“inner”、”outer”、”left”、”right”其中之一，默认为inner</td> 
  </tr> 
  <tr> 
   <td align="left">on</td> 
   <td align="left">用于连接的列名</td> 
  </tr> 
  <tr> 
   <td align="left">left_on</td> 
   <td align="left">左侧DataFrame中用作连接键的列</td> 
  </tr> 
  <tr> 
   <td align="left">right_on</td> 
   <td align="left">右侧DataFrame中用作连接键的列</td> 
  </tr> 
  <tr> 
   <td align="left">left_index</td> 
   <td align="left">将左侧DataFrame中的行索引作为连接的键</td> 
  </tr> 
  <tr> 
   <td align="left">right_index</td> 
   <td align="left">将右侧DataFrame中的行索引作为连接的键</td> 
  </tr> 
  <tr> 
   <td align="left">sort</td> 
   <td align="left">根据连接键对合并后的数据进行排序</td> 
  </tr> 
 </tbody> 
</table>

举例如下

In [5]:  df1 = DataFrame({
       'key':['b','b','a','c','a','a','b'],'data1':range(7)})
    In [6]: df1
    Out[6]:
       data1 key
    0      0   b
    1      1   b
    2      2   a
    3      3   c
    4      4   a
    5      5   a
    6      6   b
    
    In [7]: df2 = DataFrame({
       'key':['a','b','d'],'data2':range(3)})
    In [8]: df2
    Out[8]:
       data2 key
    0      0   a
    1      1   b
    2      2   d
    
    In [9]: pd.merge(df1,df2)   #默认内链接，合并相同的key即a,b
    Out[9]:
       data1 key  data2
    0      0   b      1
    1      1   b      1
    2      6   b      1
    3      2   a      0
    4      4   a      0
    5      5   a      0
    
    In [10]: df3 = DataFrame({
       'lkey':['b','b','a','c','a','a','b'],'data1':range(7)})
    In [11]: df4 = DataFrame({
       'rkey':['a','b','d'],'data2':range(3)})
    
    In [12]: df3
    Out[12]:
       data1 lkey
    0      0    b
    1      1    b
    2      2    a
    3      3    c
    4      4    a
    5      5    a
    6      6    b
    
    In [13]: df4
    Out[13]:
       data2 rkey
    0      0    a
    1      1    b
    2      2    d
    
    In [14]: print pd.merge(df3,df4,left_on = 'lkey',right_on = 'rkey')
       data1 lkey  data2 rkey
    0      0    b      1    b
    1      1    b      1    b
    2      6    b      1    b
    3      2    a      0    a
    4      4    a      0    a
    5      5    a      0    a
    
    In [15]: print pd.merge(df3,df4,left_on = 'lkey',right_on = 'data2')
    Empty DataFrame
    Columns: [data1, lkey, data2, rkey]
    Index: []
    
    In [16]: print pd.merge(df1,df2,how = 'outer')
       data1 key  data2
    0    0.0   b    1.0
    1    1.0   b    1.0
    2    6.0   b    1.0
    3    2.0   a    0.0
    4    4.0   a    0.0
    5    5.0   a    0.0
    6    3.0   c    NaN
    7    NaN   d    2.0
    
    In [17]: df5 = DataFrame({
       'key':list('bbacab'),'data1':range(6)})
    In [18]: df6 = DataFrame({
       'key':list('ababd'),'data2':range(5)})
    In [19]: df5
    Out[19]:
       data1 key
    0      0   b
    1      1   b
    2      2   a
    3      3   c
    4      4   a
    5      5   b
    
    In [20]: df6
    Out[20]:
       data2 key
    0      0   a
    1      1   b
    2      2   a
    3      3   b
    4      4   d
    
    In [21]: print pd.merge(df5,df6,on = 'key',how = 'left')
        data1 key  data2
    0       0   b    1.0
    1       0   b    3.0
    2       1   b    1.0
    3       1   b    3.0
    4       2   a    0.0
    5       2   a    2.0
    6       3   c    NaN
    7       4   a    0.0
    8       4   a    2.0
    9       5   b    1.0
    10      5   b    3.0
    
    In [22]: left = DataFrame({
       'key1':['foo','foo','bar'],'key2':['one','two','one'],'lval':[1,2,3]})
    In [23]: right = DataFrame({
       'key1':['foo','foo','bar','bar'],'key2':['one','one','one','two'],'rval':[4,5,6,7]})
    In [24]: left
    Out[24]:
      key1 key2  lval
    0  foo  one     1
    1  foo  two     2
    2  bar  one     3
    
    In [25]: right
    Out[25]:
      key1 key2  rval
    0  foo  one     4
    1  foo  one     5
    2  bar  one     6
    3  bar  two     7
    
    In [26]: print pd.merge(left,right,on = ['key1','key2'],how = 'outer')
      key1 key2  lval  rval
    0  foo  one   1.0   4.0
    1  foo  one   1.0   5.0
    2  foo  two   2.0   NaN
    3  bar  one   3.0   6.0
    4  bar  two   NaN   7.0
    
    In [27]: print pd.merge(left,right,on = 'key1')
      key1 key2_x  lval key2_y  rval
    0  foo    one     1    one     4
    1  foo    one     1    one     5
    2  foo    two     2    one     4
    3  foo    two     2    one     5
    4  bar    one     3    one     6
    5  bar    one     3    two     7
    
    In [28]: print pd.merge(left,right,on = 'key1',suffixes = ('_left','_right'))
      key1 key2_left  lval key2_right  rval
    0  foo       one     1        one     4
    1  foo       one     1        one     5
    2  foo       two     2        one     4
    3  foo       two     2        one     5
    4  bar       one     3        one     6
    5  bar       one     3        two     7

#### 5. 离散化面元划分 ####

In [17]: age = [20,22,25,27,21,23,37,31,61,45,41,32]
    In [18]: bins = [18,25,35,60,100]
    
    In [19]: cats = pd.cut(age,bins)
    In [20]: cats
    Out[20]:
    [(18, 25], (18, 25], (18, 25], (25, 35], (18, 25], ..., (25, 35], (60, 100], (35, 60], (35, 60], (25, 35]]
    Length: 12
    Categories (4, object): [(18, 25] < (25, 35] < (35, 60] < (60, 100]]
    
    In [26]:  group_names = ['YoungAdult','Adult','MiddleAged','Senior']
    
    In [27]: pd.cut(age,bins,labels = group_names)  #设置面元名称
    Out[27]:
    [YoungAdult, YoungAdult, YoungAdult, Adult, YoungAdult, ..., Adult, Senior, MiddleAged, MiddleAged, Adult]
    Length: 12
    Categories (4, object): [YoungAdult < Adult < MiddleAged < Senior]
    
    In [28]: data = np.random.randn(10)
    
    In [29]: cats = pd.qcut(data,4)   #qcut提供根据样本分位数对数据进行面元划分
    In [30]: cats
    Out[30]:
    [(0.268, 0.834], (-0.115, 0.268], (0.268, 0.834], [-1.218, -0.562], (-0.562, -0.115], [-1.218, -0.562], (-0.115, 0.268], [-1.218, -0.562], (0.268, 0.834], (-0.562, -0.115]]
    Categories (4, object): [[-1.218, -0.562] < (-0.562, -0.115] < (-0.115, 0.268] < (0.268, 0.834]]
    
    
    In [33]: pd.value_counts(cats)
    Out[33]:
    (0.268, 0.834]      3
    [-1.218, -0.562]    3
    (-0.115, 0.268]     2
    (-0.562, -0.115]    2
    dtype: int64
    
    In [35]:  pd.qcut(data,[0.1,0.5,0.9,1.])  #自定义分位数，[0-1]的数值
    Out[35]:
    [(-0.115, 0.432], (-0.115, 0.432], (0.432, 0.834], NaN, [-0.787, -0.115], [-0.787, -0.115], (-0.115, 0.432], [-0.787, -0.115], (-0.115, 0.432], [-0.787, -0.115]]
    Categories (3, object): [[-0.787, -0.115] < (-0.115, 0.432] < (0.432, 0.834]]

#### 6. 重命名轴索引 ####

In [36]: data = DataFrame(np.arange(12).reshape(3,4),index = ['Ohio','Colorado','New York'],columns = ['one','two','thr ...: ee','four'])
    
    In [37]: data
    Out[37]:
              one  two  three  four
    Ohio        0    1      2     3
    Colorado    4    5      6     7
    New York    8    9     10    11
    
    In [38]: data.index = data.index.map(str.upper)
    In [39]: data
    Out[39]:
              one  two  three  four
    OHIO        0    1      2     3
    COLORADO    4    5      6     7
    NEW YORK    8    9     10    11
    
    In [40]: data.rename(index = str.title,columns=str.upper)
    Out[40]:
              ONE  TWO  THREE  FOUR
    Ohio        0    1      2     3
    Colorado    4    5      6     7
    New York    8    9     10    11
    
    In [41]: data.rename(index={
       'OHIO':'INDIANA'},columns={
       'three':'ryana'})  #对部分轴标签更新
    Out[41]:
              one  two  ryana  four
    INDIANA     0    1      2     3
    COLORADO    4    5      6     7
    NEW YORK    8    9     10    11