pandas 中Series的map函数

Series的map方法可以接受一个函数或含有映射关系的字典型对象。 
使用map是一种实现元素级转换以及其他数据清理工作的便捷方式。 
（DataFrame中对应的是applymap()函数，当然DataFrame还有apply()函数）

1.字典映射

import pandas as pdfrom pandas import Series, DataFramedata = DataFrame({'food':['bacon','pulled pork','bacon','Pastrami',            'corned beef','Bacon','pastrami','honey ham','nova lox'],                  'ounces':[4,3,12,6,7.5,8,3,5,6]})meat_to_animal = {    'bacon':'pig',    'pulled pork':'pig',    'pastrami':'cow',    'corned beef':'cow',    'honey ham':'pig',    'nova lox':'salmon'    }  data['animal'] = data['food'].map(str.lower).map(meat_to_animal) data   data['food'].map(lambda x: meat_to_animal[x.lower()])             
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2.应用函数

In [579]: import pandas as pdIn [580]: from pandas import Series, DataFrameIn [581]: index = pd.date_range('2017-08-15', periods=10)In [582]: ser = Series(list(range(10)), index=index)In [583]: serOut[583]: 2017-08-15    02017-08-16    12017-08-17    22017-08-18    32017-08-19    42017-08-20    52017-08-21    62017-08-22    72017-08-23    82017-08-24    9Freq: D, dtype: int64In [585]: ser.index.map(lambda x: x.day)Out[585]: Int64Index([15, 16, 17, 18, 19, 20, 21, 22, 23, 24], dtype='int64')In [586]: ser.index.map(lambda x: x.weekday)Out[586]: Int64Index([1, 2, 3, 4, 5, 6, 0, 1, 2, 3], dtype='int64')In [587]: ser.map(lambda x: x+10)Out[587]: 2017-08-15    102017-08-16    112017-08-17    122017-08-18    132017-08-19    142017-08-20    152017-08-21    162017-08-22    172017-08-23    182017-08-24    19Freq: D, dtype: int64In [588]: def f(x):     ...:     if x < 5:     ...:         return True     ...:     else:     ...:         return False     ...:     In [589]: ser.map(f)Out[589]: 2017-08-15     True2017-08-16     True2017-08-17     True2017-08-18     True2017-08-19     True2017-08-20    False2017-08-21    False2017-08-22    False2017-08-23    False2017-08-24    FalseFreq: D, dtype: bool