Pandas中loc,iloc函数的用法

2023-12-20 10:13:58

用loc,iloc,直接取值三种方法;对DataFrame,Series，行和列进行操作

import pandas as pd
#读取college数据集
college = pd.read_csv('data/college.csv', index_col='INSTNM')

iloc通过行标签取数索引值的下标

# 选取第61行
pd.options.display.max_rows = 6
college.iloc[60]
'''
CITY                  Anchorage
STABBR                       AK
HBCU                          0
                        ...    
UG25ABV                  0.4386
MD_EARN_WNE_P10           42500
GRAD_DEBT_MDN_SUPP      19449.5
Name: University of Alaska Anchorage, Length: 26, dtype: object
'''


# 选取多个不连续的行
college.iloc[[60, 99, 3]] #在series中取值62行，101行，5行

	CITY	STABBR	HBCU	MENONLY	WOMENONLY	RELAFFIL	SATVRMID	SATMTMID	DISTANCEONLY	UGDS	...	UGDS_2MOR	UGDS_NRA	UGDS_UNKN	PPTUG_EF	CURROPER	PCTPELL	PCTFLOAN	UG25ABV	MD_EARN_WNE_P10	GRAD_DEBT_MDN_SUPP
INSTNM
University of Alaska Anchorage	Anchorage	AK	0.0	0.0	0.0	0	NaN	NaN	0.0	12865.0	...	0.0980	0.0181	0.0457	0.4539	1	0.2385	0.2647	0.4386	42500	19449.5
International Academy of Hair Design	Tempe	AZ	0.0	0.0	0.0	0	NaN	NaN	0.0	188.0	...	0.0160	0.0000	0.0638	0.0000	0	0.7185	0.7346	0.3905	22200	10556
University of Alabama in Huntsville	Huntsville	AL	0.0	0.0	0.0	0	595.0	590.0	0.0	5451.0	...	0.0172	0.0332	0.0350	0.2146	1	0.3072	0.4596	0.2640	45500	24097

3 rows × 26 columns

# iloc可以用切片连续选取 
college.iloc[99:102] #选取99行到101行，99，100，101

	CITY	STABBR	HBCU	MENONLY	WOMENONLY	RELAFFIL	SATVRMID	SATMTMID	DISTANCEONLY	UGDS	...	UGDS_2MOR	UGDS_NRA	UGDS_UNKN	PPTUG_EF	CURROPER	PCTPELL	PCTFLOAN	UG25ABV	MD_EARN_WNE_P10	GRAD_DEBT_MDN_SUPP
INSTNM
International Academy of Hair Design	Tempe	AZ	0.0	0.0	0.0	0	NaN	NaN	0.0	188.0	...	0.0160	0.0000	0.0638	0.0000	0	0.7185	0.7346	0.3905	22200	10556
GateWay Community College	Phoenix	AZ	0.0	0.0	0.0	0	NaN	NaN	0.0	5211.0	...	0.0127	0.0161	0.0702	0.7465	1	0.3270	0.2189	0.5832	29800	7283
Mesa Community College	Mesa	AZ	0.0	0.0	0.0	0	NaN	NaN	0.0	19055.0	...	0.0205	0.0257	0.0682	0.6457	1	0.3423	0.2207	0.4010	35200	8000

3 rows × 26 columns

loc通过行标签取数索引值

# 也可以通过行标签选取
college.loc['University of Alaska Anchorage']
'''
CITY                  Anchorage
STABBR                       AK
HBCU                          0
MENONLY                       0
WOMENONLY                     0
                        ...    
PCTPELL                  0.2385
PCTFLOAN                 0.2647
UG25ABV                  0.4386
MD_EARN_WNE_P10           42500
GRAD_DEBT_MDN_SUPP      19449.5
Name: University of Alaska Anchorage, Length: 26, dtype: object
'''

用loc加列表来选取

# 也可以用loc加列表来选取
labels = ['University of Alaska Anchorage','International Academy of Hair Design','University of Alabama in Huntsville']
college.loc[labels]

	CITY	STABBR	HBCU	MENONLY	WOMENONLY	RELAFFIL	SATVRMID	SATMTMID	DISTANCEONLY	UGDS	...	UGDS_2MOR	UGDS_NRA	UGDS_UNKN	PPTUG_EF	CURROPER	PCTPELL	PCTFLOAN	UG25ABV	MD_EARN_WNE_P10	GRAD_DEBT_MDN_SUPP
INSTNM
University of Alaska Anchorage	Anchorage	AK	0.0	0.0	0.0	0	NaN	NaN	0.0	12865.0	...	0.0980	0.0181	0.0457	0.4539	1	0.2385	0.2647	0.4386	42500	19449.5
International Academy of Hair Design	Tempe	AZ	0.0	0.0	0.0	0	NaN	NaN	0.0	188.0	...	0.0160	0.0000	0.0638	0.0000	0	0.7185	0.7346	0.3905	22200	10556
University of Alabama in Huntsville	Huntsville	AL	0.0	0.0	0.0	0	595.0	590.0	0.0	5451.0	...	0.0172	0.0332	0.0350	0.2146	1	0.3072	0.4596	0.2640	45500	24097

3 rows × 26 columns

loc可以用标签连续选取start-stop

# loc可以用标签连续选取start-stop
start = 'Amridge University'
stop = 'Athens State University'
college.loc[start:stop]

	CITY	STABBR	HBCU	MENONLY	WOMENONLY	RELAFFIL	SATVRMID	SATMTMID	DISTANCEONLY	UGDS	...	UGDS_2MOR	UGDS_NRA	UGDS_UNKN	PPTUG_EF	CURROPER	PCTPELL	PCTFLOAN	UG25ABV	MD_EARN_WNE_P10	GRAD_DEBT_MDN_SUPP
INSTNM
Amridge University	Montgomery	AL	0.0	0.0	0.0	1	NaN	NaN	1.0	291.0	...	0.0000	0.0000	0.2715	0.4536	1	0.6801	0.7795	0.8540	40100	23370
University of Alabama in Huntsville	Huntsville	AL	0.0	0.0	0.0	0	595.0	590.0	0.0	5451.0	...	0.0172	0.0332	0.0350	0.2146	1	0.3072	0.4596	0.2640	45500	24097
Alabama State University	Montgomery	AL	1.0	0.0	0.0	0	425.0	430.0	0.0	4811.0	...	0.0098	0.0243	0.0137	0.0892	1	0.7347	0.7554	0.1270	26600	33118.5
The University of Alabama	Tuscaloosa	AL	0.0	0.0	0.0	0	555.0	565.0	0.0	29851.0	...	0.0261	0.0268	0.0026	0.0844	1	0.2040	0.4010	0.0853	41900	23750
Central Alabama Community College	Alexander City	AL	0.0	0.0	0.0	0	NaN	NaN	0.0	1592.0	...	0.0000	0.0000	0.0019	0.3882	1	0.5892	0.3977	0.3153	27500	16127
Athens State University	Athens	AL	0.0	0.0	0.0	0	NaN	NaN	0.0	2991.0	...	0.0174	0.0057	0.0334	0.5517	1	0.4088	0.6296	0.6410	39000	18595

6 rows × 26 columns

index.tolist()提取行索引生成列表

#index.tolist()提取行索引生成列表 在series中，多选取一行，代表，多添加一行的列名
college.iloc[[60, 49, 3]].index.tolist()#选了三行
['University of Alaska Anchorage',
 'Snead State Community College',
 'University of Alabama in Huntsville']

用iloc选取前3行和前4列

# 读取college数据集，给行索引命名为INSTNM；选取前3行和前4列
college = pd.read_csv('data/college.csv', index_col='INSTNM')
college.iloc[:3, :4]

	CITY	STABBR	HBCU	MENONLY
INSTNM
Alabama A & M University	Normal	AL	1.0	0.0
University of Alabama at Birmingham	Birmingham	AL	0.0	0.0
Amridge University	Montgomery	AL	0.0	0.0

用loc选取前3行和前4列

	CITY	STABBR	HBCU	MENONLY
INSTNM
Alabama A & M University	Normal	AL	1.0	0.0
University of Alabama at Birmingham	Birmingham	AL	0.0	0.0
Amridge University	Montgomery	AL	0.0	0.0

选取两列的所有的行

college.iloc[:, [4,6]].head()
college.loc[:, ['WOMENONLY', 'SATVRMID']].head()

	WOMENONLY	SATVRMID
INSTNM
Alabama A & M University	0.0	424.0
University of Alabama at Birmingham	0.0	570.0
Amridge University	0.0	NaN
University of Alabama in Huntsville	0.0	595.0
Alabama State University	0.0	425.0

选取不连续的行和列

# 选取不连续的行和列
college.iloc[[100, 200], [7, 15]]

	                                  SATMTMID	UGDS_NHPI
INSTNM		
GateWay Community College	            NaN	     0.0029
American Baptist Seminary of the West	NaN	     NaN

不用loc,iloc行切片

#从行索引10到20，每隔一个取一行
# 读取college数据集；从行索引10到20，每隔一个取一行
college = pd.read_csv('data/college.csv', index_col='INSTNM')
college[10:20:2]

	CITY	STABBR	HBCU	MENONLY	WOMENONLY	RELAFFIL	SATVRMID	SATMTMID	DISTANCEONLY	UGDS	...	UGDS_2MOR	UGDS_NRA	UGDS_UNKN	PPTUG_EF	CURROPER	PCTPELL	PCTFLOAN	UG25ABV	MD_EARN_WNE_P10	GRAD_DEBT_MDN_SUPP
INSTNM
Birmingham Southern College	Birmingham	AL	0.0	0.0	0.0	1	560.0	560.0	0.0	1180.0	...	0.0051	0.0000	0.0051	0.0017	1	0.1920	0.4809	0.0152	44200	27000
Concordia College Alabama	Selma	AL	1.0	0.0	0.0	1	420.0	400.0	0.0	322.0	...	0.0031	0.0466	0.0000	0.1056	1	0.8667	0.9333	0.2367	19900	PrivacySuppressed
Enterprise State Community College	Enterprise	AL	0.0	0.0	0.0	0	NaN	NaN	0.0	1729.0	...	0.0254	0.0012	0.0069	0.3823	1	0.4895	0.2263	0.3399	24600	8273
Faulkner University	Montgomery	AL	0.0	0.0	0.0	1	NaN	NaN	0.0	2367.0	...	0.0173	0.0182	0.0258	0.2302	1	0.5812	0.7253	0.4589	37200	22000
New Beginning College of Cosmetology	Albertville	AL	0.0	0.0	0.0	0	NaN	NaN	0.0	115.0	...	0.0000	0.0000	0.0000	0.0783	1	0.8224	0.8553	0.3933	NaN	5500

5 rows × 26 columns

Series切片求10到19之间，每隔2个间隔的值

# Series也可以进行同样的切片
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
'''

查看第4002个行索引标签

# 查看第4002个行索引标签
college.index[4001]
#'Spokane Community College'

对DataFrame用标签切片

# Series和DataFrame都可以用标签进行切片。下面是对DataFrame用标签切片
start = 'Mesa Community College'
stop = 'Spokane Community College'
college[start:stop:1500]

CITY	STABBR	HBCU	MENONLY	WOMENONLY	RELAFFIL	SATVRMID	SATMTMID	DISTANCEONLY	UGDS	...	UGDS_2MOR	UGDS_NRA	UGDS_UNKN	PPTUG_EF	CURROPER	PCTPELL	PCTFLOAN	UG25ABV	MD_EARN_WNE_P10	GRAD_DEBT_MDN_SUPP
INSTNM
Mesa Community College	Mesa	AZ	0.0	0.0	0.0	0	NaN	NaN	0.0	19055.0	...	0.0205	0.0257	0.0682	0.6457	1	0.3423	0.2207	0.4010	35200	8000
Hair Academy Inc-New Carrollton	New Carrollton	MD	0.0	0.0	0.0	0	NaN	NaN	0.0	504.0	...	0.0000	0.0000	0.0000	0.4683	1	0.9756	1.0000	0.5882	15200	9666
National College of Natural Medicine	Portland	OR	0.0	0.0	0.0	0	NaN	NaN	0.0	NaN	...	NaN	NaN	NaN	NaN	1	NaN	NaN	NaN	NaN	PrivacySuppressed

3 rows × 26 columns

对Series用标签切片

# 下面是对Series用标签切片
city[start:stop:1500]
’‘’
INSTNM
Mesa Community College                            Mesa
Hair Academy Inc-New Carrollton         New Carrollton
National College of Natural Medicine          Portland
Name: CITY, dtype: object
‘’‘

直接切片不能用于列，只能用于DataFrame的行和Series，也不能同时选取行和列。

# 下面尝试选取两列，导致错误
# college[:10, ['CITY', 'STABBR']]
# TypeError: '(slice(None, 10, None), ['CITY', 'STABBR'])' is an invalid key

# 只能用.loc和.iloc选取
first_ten_instnm = college.index[:10]
college.loc[first_ten_instnm, ['CITY', 'STABBR']]

	CITY	STABBR
INSTNM
A & W Healthcare Educators	New Orleans	LA
A T Still University of Health Sciences	Kirksville	MO
ABC Beauty Academy	Garland	TX
ABC Beauty College Inc	Arkadelphia	AR
AI Miami International University of Art and Design	Miami	FL

码农公寓

iloc通过行标签取数 索引值的下标

loc通过行标签取数 索引值

不用loc,iloc行切片

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iloc通过行标签取数索引值的下标

loc通过行标签取数索引值