選取數據子集

簡書大神SeanCheney的譯作，我作了些格式調整和文章目錄結構的變化，更適合自己閱讀，以后翻閱是更加方便自己查找吧

import pandas as pd import numpy as np

設定最大列數和最大行數

pd.set_option('max_columns',5 , 'max_rows', 5)

1 選取Series數據

college = pd.read_csv('data/college.csv', index_col='INSTNM') city = college['CITY']

1.1 iloc整數選取

標量

city.iloc[3] 'Huntsville'

多行 - 整數列表

city.iloc[[10,20,30]] INSTNM Birmingham Southern College Birmingham George C Wallace State Community College-Hanceville Hanceville Judson College Marion Name: CITY, dtype: object

多行 - 整數切片

city.iloc[4:50:10] INSTNM Alabama State University Montgomery Enterprise State Community College Enterprise Heritage Christian University Florence Marion Military Institute Marion Reid State Technical College Evergreen Name: CITY, dtype: object

1.2 loc標簽選取

標量

city.loc['Heritage Christian University'] 'Florence'

多行 - 標簽列表

隨機選擇4個標簽

labels = list(np.random.choice(city.index, 4)) labels ['University of St Thomas','Paul Mitchell the School-Woodbridge','San Francisco Conservatory of Music','Trinity Bible College'] city.loc[labels] INSTNM University of St Thomas Saint Paul Paul Mitchell the School-Woodbridge Woodbridge San Francisco Conservatory of Music San Francisco Trinity Bible College Ellendale Name: CITY, dtype: object

多行 - 標簽切片

city.loc['Alabama State University':'Reid State Technical College':10] INSTNM Alabama State University Montgomery Enterprise State Community College Enterprise Heritage Christian University Florence Marion Military Institute Marion Reid State Technical College Evergreen Name: CITY, dtype: object

也可以切片逆序選取

city.loc['Reid State Technical College':'Alabama State University':-10] INSTNM Reid State Technical College Evergreen Marion Military Institute Marion Heritage Christian University Florence Enterprise State Community College Enterprise Alabama State University Montgomery Name: CITY, dtype: object

2 選取DataFrame數據

2.1 選取DataFrame的行

注意iloc是整數索引，loc是標簽索引即可

2.2 同時選取DataFrame的行和列

2.2.1 選取前3行和前4列

college.iloc[:3, :4] CITYSTABBRHBCUMENONLYINSTNMAlabama A & M UniversityUniversity of Alabama at BirminghamAmridge University

Normal	AL	1.0	0.0
Birmingham	AL	0.0	0.0
Montgomery	AL	0.0	0.0

college.loc[:'Amridge University', :'MENONLY'] CITYSTABBRHBCUMENONLYINSTNMAlabama A & M UniversityUniversity of Alabama at BirminghamAmridge University

Normal	AL	1.0	0.0
Birmingham	AL	0.0	0.0
Montgomery	AL	0.0	0.0

2.2.2 選取兩列的所有的行

college.iloc[:, [4,6]].head() WOMENONLYSATVRMIDINSTNMAlabama A & M UniversityUniversity of Alabama at BirminghamAmridge UniversityUniversity of Alabama in HuntsvilleAlabama State University

0.0	424.0
0.0	570.0
0.0	NaN
0.0	595.0
0.0	425.0

college.loc[:, ['WOMENONLY', 'SATVRMID']] WOMENONLYSATVRMIDINSTNMAlabama A & M UniversityUniversity of Alabama at Birmingham...Bay Area Medical Academy - San Jose Satellite LocationExcel Learning Center-San Antonio South

0.0	424.0
0.0	570.0
...	...
NaN	NaN
NaN	NaN

7535 rows × 2 columns

2.2.3 選取不連續的行和列

college.iloc[[100, 200], [7, 15]] SATMTMIDUGDS_NHPIINSTNMGateWay Community CollegeAmerican Baptist Seminary of the West

NaN	0.0029
NaN	NaN

rows = ['GateWay Community College', 'American Baptist Seminary of the West'] columns = ['SATMTMID', 'UGDS_NHPI'] college.loc[rows, columns] SATMTMIDUGDS_NHPIINSTNMGateWay Community CollegeAmerican Baptist Seminary of the West

NaN	0.0029
NaN	NaN

2.2.4 選取一個標量值

college.iloc[5, -4] 0.401 college.loc['The University of Alabama', 'PCTFLOAN'] 0.401

2.2.5 行切片選取一列

college.iloc[90:80:-2, 5] INSTNM Empire Beauty School-Flagstaff 0 Charles of Italy Beauty College 0 Central Arizona College 0 University of Arizona 0 Arizona State University-Tempe 0 Name: RELAFFIL, dtype: int64 start = 'Empire Beauty School-Flagstaff' stop = 'Arizona State University-Tempe' college.loc[start:stop:-2, 'RELAFFIL'] INSTNM Empire Beauty School-Flagstaff 0 Charles of Italy Beauty College 0 Central Arizona College 0 University of Arizona 0 Arizona State University-Tempe 0 Name: RELAFFIL, dtype: int64

3 用整數和標簽的互換

用索引方法get_loc，找到指定列的整數位置

col_start = college.columns.get_loc('UGDS_WHITE') col_end = college.columns.get_loc('UGDS_UNKN') + 1 col_start, col_end (10, 19) college.iloc[:5, col_start:col_end] UGDS_WHITEUGDS_BLACK...UGDS_NRAUGDS_UNKNINSTNMAlabama A & M UniversityUniversity of Alabama at BirminghamAmridge UniversityUniversity of Alabama in HuntsvilleAlabama State University

0.0333	0.9353	...	0.0059	0.0138
0.5922	0.2600	...	0.0179	0.0100
0.2990	0.4192	...	0.0000	0.2715
0.6988	0.1255	...	0.0332	0.0350
0.0158	0.9208	...	0.0243	0.0137

5 rows × 9 columns

獲得整數行對應的標簽名

row_end = college.index[4] col_start,col_end = college.columns[10],college.columns[19] col_start,col_end ('UGDS_WHITE', 'PPTUG_EF') college.loc[:row_end, col_start:col_end] UGDS_WHITEUGDS_BLACK...UGDS_UNKNPPTUG_EFINSTNMAlabama A & M UniversityUniversity of Alabama at BirminghamAmridge UniversityUniversity of Alabama in HuntsvilleAlabama State University

0.0333	0.9353	...	0.0138	0.0656
0.5922	0.2600	...	0.0100	0.2607
0.2990	0.4192	...	0.2715	0.4536
0.6988	0.1255	...	0.0350	0.2146
0.0158	0.9208	...	0.0137	0.0892

5 rows × 10 columns

4 切片操作

4.1 惰性行切片

惰性,我的理解就就是省去loc和iloc吧，但是惰性切片不能用于列，只能用于DataFrame的行和Series，也不能同時選取行和列。

Series選取數據

city = college['CITY'] city[10:20:2] INSTNM Birmingham Southern College Birmingham Concordia College Alabama Selma Enterprise State Community College Enterprise Faulkner University Montgomery New Beginning College of Cosmetology Albertville Name: CITY, dtype: object

dataframe行選取

college[10:20:2] CITYSTABBR...MD_EARN_WNE_P10GRAD_DEBT_MDN_SUPPINSTNMBirmingham Southern CollegeConcordia College AlabamaEnterprise State Community CollegeFaulkner UniversityNew Beginning College of Cosmetology

Birmingham	AL	...	44200	27000
Selma	AL	...	19900	PrivacySuppressed
Enterprise	AL	...	24600	8273
Montgomery	AL	...	37200	22000
Albertville	AL	...	NaN	5500

5 rows × 26 columns

Series和DataFrame都可以用標簽進行切片。

start = 'Mesa Community College' stop = 'Spokane Community College' college[start:stop:1500] CITYSTABBR...MD_EARN_WNE_P10GRAD_DEBT_MDN_SUPPINSTNMMesa Community CollegeHair Academy Inc-New CarrolltonNational College of Natural Medicine

Mesa	AZ	...	35200	8000
New Carrollton	MD	...	15200	9666
Portland	OR	...	NaN	PrivacySuppressed

3 rows × 26 columns

4.2 按照字母切片

需先對索引進行排序

college = college.sort_index() college.head() CITYSTABBR...MD_EARN_WNE_P10GRAD_DEBT_MDN_SUPPINSTNMA & W Healthcare EducatorsA T Still University of Health SciencesABC Beauty AcademyABC Beauty College IncAI Miami International University of Art and Design

New Orleans	LA	...	NaN	19022.5
Kirksville	MO	...	219800	PrivacySuppressed
Garland	TX	...	NaN	PrivacySuppressed
Arkadelphia	AR	...	PrivacySuppressed	16500
Miami	FL	...	29900	31000

5 rows × 26 columns

選取字母順序在‘Sp’和‘Su’之間的學校

college.loc['Sp':'Su'] CITYSTABBR...MD_EARN_WNE_P10GRAD_DEBT_MDN_SUPPINSTNMSpa Tech Institute-IpswichSpa Tech Institute-Plymouth...Styles and Profiles Beauty CollegeStyletrends Barber and Hairstyling Academy

Ipswich	MA	...	21500	6333
Plymouth	MA	...	21500	6333
...	...	...	...	...
Selmer	TN	...	PrivacySuppressed	PrivacySuppressed
Rock Hill	SC	...	PrivacySuppressed	9495.5

201 rows × 26 columns

轉載于:https://www.cnblogs.com/shiyushiyu/p/9742232.html

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