DataFrame.iterrows的一种用法

import pandas as pd

import numpy as np

help(pd.DataFrame.iterrows)

Help on function iterrows in module pandas.core.frame:

iterrows(self)
    Iterate over DataFrame rows as (index, Series) pairs.
    
    Notes
    -----
    
    1. Because ``iterrows`` returns a Series for each row,
       it does **not** preserve dtypes across the rows (dtypes are
       preserved across columns for DataFrames). For example,
    
       >>> df = pd.DataFrame([[1, 1.5]], columns=['int', 'float'])
       >>> row = next(df.iterrows())[1]
       >>> row
       int      1.0
       float    1.5
       Name: 0, dtype: float64
       >>> print(row['int'].dtype)
       float64
       >>> print(df['int'].dtype)
       int64
    
       To preserve dtypes while iterating over the rows, it is better
       to use :meth:`itertuples` which returns namedtuples of the values
       and which is generally faster than ``iterrows``.
    
    2. You should **never modify** something you are iterating over.
       This is not guaranteed to work in all cases. Depending on the
       data types, the iterator returns a copy and not a view, and writing
       to it will have no effect.
    
    Returns
    -------
    it : generator
        A generator that iterates over the rows of the frame.
    
    See also
    --------
    itertuples : Iterate over DataFrame rows as namedtuples of the values.
    iteritems : Iterate over (column name, Series) pairs.

​

运用iterrows()返回的index和row,其中index是行索引，row是包含改行信息的Series的迭代器。运用这个方法，可以一行一行的增加特殊要求的列（前提是首先初始化该特殊要求的列）

xx=np.random.randint(9,size=(6,3))

tests=pd.DataFrame(xx,columns=['one','two','three']);tests

	one	two	three
0	3	0	4
1	1	0	3
2	1	4	4
3	7	3	2
4	7	5	0
5	5	8	8

现在我们想加上一列，这一列的要求如下：如果同行的'one'+'two'+'three'是奇数，则写上奇数，如果是偶数，则写上偶数。

tests['special']='ini'

for index,row in tests.iterrows():
    num=(row.values[:-1]).sum()
    if num%2 :
        row['special']='奇数'
    else:
        row['special']='偶数'
    tests.loc[index]=row          #将Series 迭代器row赋值给tests的index行

tests

	one	two	three	special
0	3	0	4	奇数
1	1	0	3	偶数
2	1	4	4	奇数
3	7	3	2	偶数
4	7	5	0	偶数
5	5	8	8	奇数