Introduction

我们经常会收到一些带有列名、索引名或其他命名约定的数据，而这些约定我们并不满意。在这种情况下，您将学习如何使用 Pandas 函数将有问题的条目更改为更合适的名称。

您还将学习如何合并来自多个 DataFrame 和/或 Series 的数据。

要开始本主题的练习，请点击此处。

Renaming

我们首先要介绍的函数是 rename()，它允许你更改索引名称和/或列名称。例如，要将数据集中的 points 列更改为 score，我们可以这样做：

In [1]:

import pandas as pd
pd.set_option('display.max_rows', 5)
reviews = pd.read_csv("../input/wine-reviews/winemag-data-130k-v2.csv", index_col=0)

In [2]:

reviews.rename(columns={'points': 'score'})

Out[2]:

	country	description	designation	score	price	province	region_1	region_2	taster_name	taster_twitter_handle	title	variety	winery
0	Italy	Aromas include tropical fruit, broom, brimston…	Vulkà Bianco	87	NaN	Sicily & Sardinia	Etna	NaN	Kerin O’Keefe	@kerinokeefe	Nicosia 2013 Vulkà Bianco (Etna)	White Blend	Nicosia
1	Portugal	This is ripe and fruity, a wine that is smooth…	Avidagos	87	15.0	Douro	NaN	NaN	Roger Voss	@vossroger	Quinta dos Avidagos 2011 Avidagos Red (Douro)	Portuguese Red	Quinta dos Avidagos
…	…	…	…	…	…	…	…	…	…	…	…	…	…
129969	France	A dry style of Pinot Gris, this is crisp with …	NaN	90	32.0	Alsace	Alsace	NaN	Roger Voss	@vossroger	Domaine Marcel Deiss 2012 Pinot Gris (Alsace)	Pinot Gris	Domaine Marcel Deiss
129970	France	Big, rich and off-dry, this is powered by inte…	Lieu-dit Harth Cuvée Caroline	90	21.0	Alsace	Alsace	NaN	Roger Voss	@vossroger	Domaine Schoffit 2012 Lieu-dit Harth Cuvée Car…	Gewürztraminer	Domaine Schoffit

129971 行 × 13 列

rename() 函数允许您通过分别指定 index 或 column 关键字参数来重命名索引或列的值。它支持多种输入格式，但通常使用 Python 字典最为方便。以下是使用它重命名索引中某些元素的示例。

In [3]:

reviews.rename(index={0: 'firstEntry', 1: 'secondEntry'})

Out[3]:

	country	description	designation	points	price	province	region_1	region_2	taster_name	taster_twitter_handle	title	variety	winery
firstEntry	Italy	Aromas include tropical fruit, broom, brimston…	Vulkà Bianco	87	NaN	Sicily & Sardinia	Etna	NaN	Kerin O’Keefe	@kerinokeefe	Nicosia 2013 Vulkà Bianco (Etna)	White Blend	Nicosia
secondEntry	Portugal	This is ripe and fruity, a wine that is smooth…	Avidagos	87	15.0	Douro	NaN	NaN	Roger Voss	@vossroger	Quinta dos Avidagos 2011 Avidagos Red (Douro)	Portuguese Red	Quinta dos Avidagos
…	…	…	…	…	…	…	…	…	…	…	…	…	…
129969	France	A dry style of Pinot Gris, this is crisp with …	NaN	90	32.0	Alsace	Alsace	NaN	Roger Voss	@vossroger	Domaine Marcel Deiss 2012 Pinot Gris (Alsace)	Pinot Gris	Domaine Marcel Deiss
129970	France	Big, rich and off-dry, this is powered by inte…	Lieu-dit Harth Cuvée Caroline	90	21.0	Alsace	Alsace	NaN	Roger Voss	@vossroger	Domaine Schoffit 2012 Lieu-dit Harth Cuvée Car…	Gewürztraminer	Domaine Schoffit

129971 行 × 13 列

您可能经常重命名列，但很少重命名索引值。因此，使用 set_index() 通常更方便。

行索引和列索引都可以拥有各自的 name 属性。可以使用配套的 rename_axis() 方法来更改这些名称。例如：

In [4]:

reviews.rename_axis("wines", axis='rows').rename_axis("fields", axis='columns')

Out[4]:

fields	country	description	designation	points	price	province	region_1	region_2	taster_name	taster_twitter_handle	title	variety	winery
wines
0	Italy	Aromas include tropical fruit, broom, brimston…	Vulkà Bianco	87	NaN	Sicily & Sardinia	Etna	NaN	Kerin O’Keefe	@kerinokeefe	Nicosia 2013 Vulkà Bianco (Etna)	White Blend	Nicosia
1	Portugal	This is ripe and fruity, a wine that is smooth…	Avidagos	87	15.0	Douro	NaN	NaN	Roger Voss	@vossroger	Quinta dos Avidagos 2011 Avidagos Red (Douro)	Portuguese Red	Quinta dos Avidagos
…	…	…	…	…	…	…	…	…	…	…	…	…	…
129969	France	A dry style of Pinot Gris, this is crisp with …	NaN	90	32.0	Alsace	Alsace	NaN	Roger Voss	@vossroger	Domaine Marcel Deiss 2012 Pinot Gris (Alsace)	Pinot Gris	Domaine Marcel Deiss
129970	France	Big, rich and off-dry, this is powered by inte…	Lieu-dit Harth Cuvée Caroline	90	21.0	Alsace	Alsace	NaN	Roger Voss	@vossroger	Domaine Schoffit 2012 Lieu-dit Harth Cuvée Car…	Gewürztraminer	Domaine Schoffit

129971 行 × 13 列

Combining

在对数据集执行操作时，我们有时需要以非同寻常的方式组合不同的 DataFrame 和/或 Series。Pandas 提供了三种核心方法来实现这一点。按复杂度依次递增，这三种方法分别是 concat()、join() 和 merge()。merge() 的大部分功能也可以用 join() 更简单地实现，因此我们将省略它，并重点介绍前两个函数。

最简单的组合方法是 concat()。给定一个元素列表，此函数会沿某个轴将这些元素合并在一起。

当数据位于不同的 DataFrame 或 Series 对象中，但具有相同的字段（列）时，这种方法非常有用。例如：YouTube 视频数据集，它根据原产国（例如，本例中为加拿大和英国）对数据进行拆分。如果我们想同时研究多个国家/地区，可以使用 concat() 将它们合并在一起：

In [5]:

canadian_youtube = pd.read_csv("../input/youtube-new/CAvideos.csv")
british_youtube = pd.read_csv("../input/youtube-new/GBvideos.csv")

pd.concat([canadian_youtube, british_youtube])

Out[5]:

	video_id	trending_date	title	channel_title	category_id	publish_time	tags	views	likes	dislikes	comment_count	thumbnail_link	comments_disabled	ratings_disabled	video_error_or_removed	description
0	n1WpP7iowLc	17.14.11	Eminem - Walk On Water (Audio) ft. Beyoncé	EminemVEVO	10	2017-11-10T17:00:03.000Z	Eminem\|”Walk”\|”On”\|”Water”\|”Aftermath/Shady/In…	17158579	787425	43420	125882	https://i.ytimg.com/vi/n1WpP7iowLc/default.jpg	False	False	False	Eminem’s new track Walk on Water ft. Beyoncé i…
1	0dBIkQ4Mz1M	17.14.11	PLUSH - Bad Unboxing Fan Mail	iDubbbzTV	23	2017-11-13T17:00:00.000Z	plush\|”bad unboxing”\|”unboxing”\|”fan mail”\|”id…	1014651	127794	1688	13030	https://i.ytimg.com/vi/0dBIkQ4Mz1M/default.jpg	False	False	False	STill got a lot of packages. Probably will las…
…	…	…	…	…	…	…	…	…	…	…	…	…	…	…	…	…
38914	-DRsfNObKIQ	18.14.06	Eleni Foureira - Fuego - Cyprus - LIVE - First…	Eurovision Song Contest	24	2018-05-08T20:32:32.000Z	Eurovision Song Contest\|”2018”\|”Lisbon”\|”Cypru…	14317515	151870	45875	26766	https://i.ytimg.com/vi/-DRsfNObKIQ/default.jpg	False	False	False	Eleni Foureira represented Cyprus at the first…
38915	4YFo4bdMO8Q	18.14.06	KYLE - Ikuyo feat. 2 Chainz & Sophia Black [A…	SuperDuperKyle	10	2018-05-11T04:06:35.000Z	Kyle\|”SuperDuperKyle”\|”Ikuyo”\|”2 Chainz”\|”Soph…	607552	18271	274	1423	https://i.ytimg.com/vi/4YFo4bdMO8Q/default.jpg	False	False	False	Debut album ‘Light of Mine’ out now: http://ky…

79797 行 × 16 列

就复杂度而言，中间的组合器是 join()。join() 可以组合具有共同索引的不同 DataFrame 对象。例如，要提取恰好在同一天在加拿大和英国都流行的视频，我们可以执行以下操作：

In [6]:

left = canadian_youtube.set_index(['title', 'trending_date'])
right = british_youtube.set_index(['title', 'trending_date'])

left.join(right, lsuffix='_CAN', rsuffix='_UK')

Out[6]:

		video_id_CAN	channel_title_CAN	category_id_CAN	publish_time_CAN	tags_CAN	views_CAN	likes_CAN	dislikes_CAN	comment_count_CAN	thumbnail_link_CAN	…	tags_UK	views_UK	likes_UK	dislikes_UK	comment_count_UK	thumbnail_link_UK	comments_disabled_UK	ratings_disabled_UK	video_error_or_removed_UK	description_UK
title	trending_date
!! THIS VIDEO IS NOTHING BUT PAIN !! \| Getting Over It - Part 7	18.04.01	PNn8sECd7io	Markiplier	20	2018-01-03T19:33:53.000Z	getting over it\|”markiplier”\|”funny moments”\|”…	835930	47058	1023	8250	https://i.ytimg.com/vi/PNn8sECd7io/default.jpg	…	NaN	NaN	NaN	NaN	NaN	NaN	NaN	NaN	NaN	NaN
#1 Fortnite World Rank - 2,323 Solo Wins!	18.09.03	DvPW66IFhMI	AlexRamiGaming	20	2018-03-09T07:15:52.000Z	PS4 Battle Royale\|”PS4 Pro Battle Royale”\|”Bat…	212838	5199	542	11	https://i.ytimg.com/vi/DvPW66IFhMI/default.jpg	…	NaN	NaN	NaN	NaN	NaN	NaN	NaN	NaN	NaN	NaN
…	…	…	…	…	…	…	…	…	…	…	…	…	…	…	…	…	…	…	…	…	…	…
🚨 BREAKING NEWS 🔴 Raja Live all Slot Channels Welcome 🎰	18.07.05	Wt9Gkpmbt44	TheBigJackpot	24	2018-05-07T06:58:59.000Z	Slot Machine\|”win”\|”Gambling”\|”Big Win”\|”raja”…	28973	2167	175	10	https://i.ytimg.com/vi/Wt9Gkpmbt44/default.jpg	…	NaN	NaN	NaN	NaN	NaN	NaN	NaN	NaN	NaN	NaN
🚨Active Shooter at YouTube Headquarters - LIVE BREAKING NEWS COVERAGE	18.04.04	Az72jrKbANA	Right Side Broadcasting Network	25	2018-04-03T23:12:37.000Z	YouTube shooter\|”YouTube active shooter”\|”acti…	103513	1722	181	76	https://i.ytimg.com/vi/Az72jrKbANA/default.jpg	…	NaN	NaN	NaN	NaN	NaN	NaN	NaN	NaN	NaN	NaN

40900 行 × 28 列

此处 lsuffix 和 rsuffix 参数是必需的，因为该数据在英国和加拿大数据集中的列名相同。如果不是这样（比如说，我们事先重命名了它们），我们就不需要它们了。

Your turn

如果你还没有开始练习，你可以**从这里开始**。