Python Pandas模块介绍

╰+攻爆jí腚メ 2022-05-22 00:21 324阅读 0赞

**Pandas模块是Python用于数据导入及整理的模块，对数据挖掘前期数据的处理工作十分有用。**

**Pandas模块的数据结构主要有两：1、Series ；2、DataFrame ，下面将分别从这两方面介绍：**

**(1) Series结构介绍和操作示例：  
    1.1、介绍**

The Series is the primary building block of pandas and represents a one-dimensional labeled array based on the NumPy ndarray;
    大概就是说Series结构是基于NumPy的ndarray结构，是一个一维的标签矩阵（感觉跟python里的字典结构有点像）

**    1.2、相关操作**

# coding:utf-8
    
    print "1/**************"
    '''
    创建
    pd.Series([list]，index=[list])//以list为参数，参数为一list;index为可选参数，若不填则默认index从0开始；
    若添则index长度与value长度相等
    '''
    import pandas as pd
    s=pd.Series([1,2,3,4,5], index=['a','b','c','f','e'])
    print s
    '''
    1/**************
    a    1
    b    2
    c    3
    f    4
    e    5
    dtype: int64
    '''
    print "2/**************"
    '''
    创建
    pd.Series({dict})//以一字典结构为参数
    '''
    import pandas as pd
    s=pd.Series({'a':3,'b':4,'c':5,'f':6,'e':8})
    print s
    '''
    2/**************
    a    3
    b    4
    c    5
    e    8
    f    6
    dtype: int64
    '''
    print "3/**************"
    '''
    取值 
    s[index] or s[[index的list]] 
    取值操作类似数组，当取不连续的多个值时可以以一list为参数
    '''
    import pandas as pd
    import numpy as np
    
    v=np.random.random_sample(50)
    s=pd.Series(v)
    s1=s[[3,7,33]]
    s2=s[1:5]
    s3=s[49]
    print "s1\n",s1
    print "s2\n",s2
    print "s3\n",s3
    '''
    3/**************
    s1
    3     0.751252
    7     0.608317
    33    0.612134
    dtype: float64
    s2
    1    0.079671
    2    0.192029
    3    0.751252
    4    0.280966
    dtype: float64
    s3
    0.273614509027
    '''
    print "4/**************"
    '''
    head(n);.tail(n)//取出头n行或尾n行，n为可选参数，若不填默认5
    '''
    import pandas as pd
    import numpy as np
    
    v=np.random.random_sample(50)
    s=pd.Series(v)
    print "s.head()\n",s.head()
    print "s.head(1)\n",s.head(1)
    print "s.tail(3)\n",s.tail(3)
    '''
    4/**************
    s.head()
    0    0.585155
    1    0.938871
    2    0.107134
    3    0.479727
    4    0.641377
    dtype: float64
    s.head(1)
    0    0.585155
    dtype: float64
    s.tail(3)
    47    0.527761
    48    0.649811
    49    0.499103
    dtype: float64
    '''
    
    print "5/**************"
    '''
    .index; .values//取出index 与values ,返回list
    Size、shape、uniqueness、counts of values
    '''
    import pandas as pd
    import numpy as np
    
    v=[10,3,2,2,np.nan]
    v=pd.Series(v);
    print "v.index",v.index
    print "v.values",v.values
    print "len():",len(v)  # Series长度,包括NaN
    print "shape():",np.shape(v)  # 矩阵形状，（，）
    print "count():",v.count()  # Series长度，不包括NaN
    print "unique():",v.unique()  # 出现不重复values值
    print "value_counts():\n",v.value_counts()  # 统计value值出现次数
    
    '''
    5/**************
    v.index RangeIndex(start=0, stop=5, step=1)
    v.values [ 10.   3.   2.   2.  nan]
    len(): 5
    shape(): (5,)
    count(): 4
    unique(): [ 10.   3.   2.  nan]
    value_counts():
    2.0     2
    3.0     1
    10.0    1
    dtype: int64
    '''
    
    print "6/**************"
    '''
    加运算 
    相同index的value相加，若index并非共有的则该index对应value变为NaN
    '''
    import pandas as pd
    s1=pd.Series([1,2,3,4],index=[1,2,3,4])
    s2=pd.Series([1,1,1,1])
    s3=s1+s2
    print s3
    
    '''
    6/**************
    0    NaN
    1    2.0
    2    3.0
    3    4.0
    4    NaN
    dtype: float64
    '''

**    2.1、介绍**

DataFrame unifies two or more Series into a single data structure.Each Series then represents a named column of the DataFrame, and instead of each column having its own index, the DataFrame provides a single index and the data in all columns is aligned to the master index of the DataFrame. 
    这段话的意思是，DataFrame提供的是一个类似表的结构，由多个Series组成，而Series在DataFrame中叫columns。

![70][]

**    2.2、 相关操作**

# coding:utf-8
    '''
    create
    pd.DataFrame() 
    参数： 
    1、二维array； 
    2、Series 列表； 
    3、value为Series的字典
    注：若创建使用的参数中，array、Series长度不一样时，对应index的value值若不存在则为NaN
    '''
    print "1/**************"
    import pandas as pd
    import numpy as np
    
    s1=np.array([1,2,4])
    s2=np.array([5,6,7,8])
    print s1
    print type(s1)
    # 1、二维array；
    df=pd.DataFrame([s1,s2])
    print df
    '''
    1/**************
    [1 2 4]
    <type 'numpy.ndarray'>
       0  1  2    3
    0  1  2  4  NaN
    1  5  6  7  8.0
    '''
    print "2/**************"
    
    import pandas as pd
    import numpy as np
    
    s1=pd.Series(np.array([1,2,3,4]))
    s2=pd.Series(np.array([5,6,7,8]))
    print s1
    print type(s1)
    # 2、Series 列表；
    df=pd.DataFrame([s1,s2])
    print df
    print df.shape
    '''
    2/**************
    0    1
    1    2
    2    3
    3    4
    dtype: int64
    <class 'pandas.core.series.Series'>
       0  1  2  3
    0  1  2  3  4
    1  5  6  7  8
    (2, 4)
    '''
    print "3/**************"
    
    import pandas as pd
    import numpy as np
    
    s1=pd.Series(np.array([1,2,3,4]))
    s2=pd.Series(np.array([5,6,7,8]))
    # 3、value为Series的字典
    df=pd.DataFrame({"a":s1,"b":s2});
    print df
    print df.shape
    print df.head(2)
    print df.tail(2)
    
    print df.items
    print df.keys()
    print df.values
    print "df['a']\n", df['a']
    
    '''
    3/**************
       a  b
    0  1  5
    1  2  6
    2  3  7
    3  4  8
    (4, 2)
       a  b
    0  1  5
    1  2  6
       a  b
    2  3  7
    3  4  8
    <bound method DataFrame.iteritems of    a  b
    0  1  5
    1  2  6
    2  3  7
    3  4  8>
    Index([u'a', u'b'], dtype='object')
    [[1 5]
     [2 6]
     [3 7]
     [4 8]]
    df['a']
    0    1
    1    2
    2    3
    3    4
    '''
    '''
    b.属性
    b.1 .columns :每个columns对应的keys
    b.2 .shape:形状，（a，b）,index长度为a,columns数为b
    b.3 .index;.values:返回index列表；返回value二维array
    b.4 .head();.tail();
    '''
    print "4/**************"
    '''
    c.if-then 操作
    c.1使用.ix[]
    df.ix[条件，then操作区域]
    '''
    df=pd.DataFrame({"A":[1,2,3,4],"B":[5,6,7,8],"C":[1,1,1,1]})
    print df
    df.ix[df.A > 1,'B']= -1
    print df
    '''
    4/**************
       A  B  C
    0  1  5  1
    1  2  6  1
    2  3  7  1
    3  4  8  1
       A  B  C
    0  1  5  1
    1  2 -1  1
    2  3 -1  1
    3  4 -1  1
    '''
    print "5/**************"
    '''
    c.2使用numpy.where
    np.where(条件，then，else)
    '''
    df=pd.DataFrame({"A":[1,2,3,4],"B":[5,6,7,8],"C":[1,1,1,1]})
    print df
    print df.keys()
    df["then"]=np.where(df.A<3, 1, 0)
    print df
    print df.keys()
    '''
    5/**************
       A  B  C
    0  1  5  1
    1  2  6  1
    2  3  7  1
    3  4  8  1
    Index([u'A', u'B', u'C'], dtype='object')
       A  B  C  then
    0  1  5  1     1
    1  2  6  1     1
    2  3  7  1     0
    3  4  8  1     0
    Index([u'A', u'B', u'C', u'then'], dtype='object')
    '''
    
    '''
    d.根据条件选择取DataFrame
    '''
    print "6/**************"
    #d.1 直接取值df.[]
    
    df=pd.DataFrame({"A":[1,2,3,4],"B":[5,6,7,8],"C":[1,1,1,1]})
    df=df[df.A>=3]
    print df
    '''
    6/**************
       A  B  C
    2  3  7  1
    3  4  8  1
    
    '''
    
    print "7/**************"
    # d.2 使用.loc[]
    df=pd.DataFrame({"A":[1,2,3,4],"B":[5,6,7,8],"C":[1,1,1,1]})
    df=df.loc[df.A>2]
    print df
    
    '''
    7/**************
       A  B  C
    2  3  7  1
    3  4  8  1
    '''
    
    '''
    e.Grouping
    '''
    print "8/**************"
    # e.1 groupby 形成group
    df = pd.DataFrame({'animal': 'cat dog cat fish dog cat cat'.split(),
                      'size': list('SSMMMLL'),
                      'weight': [8, 10, 11, 1, 20, 12, 12],
                      'adult' : [False] * 5 + [True] * 2});
    print df
    
    # 列出动物中weight最大的对应size
    group=df.groupby("animal").apply(lambda subf: subf['size'][subf['weight'].idxmax()])
    print group
    '''
    8/**************
       adult animal size  weight
    0  False    cat    S       8
    1  False    dog    S      10
    2  False    cat    M      11
    3  False   fish    M       1
    4  False    dog    M      20
    5   True    cat    L      12
    6   True    cat    L      12
    animal
    cat     L
    dog     M
    fish    M
    dtype: object
    '''
    print "9/**************"
    # e.2 使用get_group 取出其中一分组
    df = pd.DataFrame({'animal': 'cat dog cat fish dog cat cat'.split(),
                      'size': list('SSMMMLL'),
                      'weight': [8, 10, 11, 1, 20, 12, 12],
                      'adult' : [False] * 5 + [True] * 2});
    
    group=df.groupby("animal")
    cat=group.get_group("cat")
    print cat
    '''
    9/**************
       adult animal size  weight
    0  False    cat    S       8
    2  False    cat    M      11
    5   True    cat    L      12
    6   True    cat    L      12
    '''

其他具体操作请参考CookBook  
http://pandas.pydata.org/pandas-docs/stable/cookbook.html  
参考:\# https://blog.csdn.net/u014607457/article/details/51290582

[70]: /images/20220522/1ed8e48bbf8a47cfa9c200bf29d22e63.png