July 2019
Intermediate to advanced
365 pages
8h 13m
Chinese
Content preview from Python机器学习手册：从数据预处理到深度学习
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56
｜
第
3
章
数据整理
#
创建
URL
url = 'https://tinyurl.com/titanic-csv'
#
加载数据
dataframe = pd.read_csv(url)
#
创建一个函数
def uppercase(x):
return x.upper()
#
应用函数，查看两行
dataframe['Name'].apply(uppercase)[0:2]
0 ALLEN, MISS ELISABETH WALTON
1 ALLISON, MISS HELEN LORAINE
Name: Name, dtype: object
讨论
在数据清洗和数据整理中，
apply
是一个功能非常强大的函数。通常需要先写一个函数
来执行某个有用的操作（例如，将姓和名分开、将字符串转换成浮点数等），然后对一
列中的所有元素应用这个函数。
3.17
对所有分组应用一个函数
问题描述
我们已经使用
groupby
对行做了分组，现在要对每一组数据应用一个函数。
解决方案
联合使用
groupby
和
apply
：
#
加载库
import pandas as pd
#
创建
URL
url = 'https://tinyurl.com/titanic-csv'
#
加载数据
dataframe = pd.read_csv(url)
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