pandas简介

pandas 是基于NumPy 的一种工具，该工具是为解决数据分析任务而创建的。Pandas 纳入了大量库和一些标准的数据模型，提供了高效地操作大型数据集所需的工具。pandas提供了大量能使我们快速便捷地处理数据的函数和方法。pandas 是 Python 的核心数据分析支持库，提供了快速、灵活、明确的数据结构，旨在简单、直观地处理关系型、标记型数据。

1.数据读取

首先，pip install pandas 安装Pandas库。

引用pandas库，通常简称为pd，如下：

import pandas as pd

1.1获取样本数据-以波士顿房价数据为例

从sklearn.datasets数据集中下载波士顿房价数据：

from sklearn.datasets import load_boston
boston = load_boston()
# 输出对boston数据集的描述
print("波士顿房价的数据集描述是\n", boston.DESCR)

运行结果：

波士顿房价的数据集描述是.. _boston_dataset:Boston house prices dataset
---------------------------
**Data Set Characteristics:**  :Number of Instances: 506 :Number of Attributes: 13 numeric/categorical predictive. Median Value (attribute 14) is usually the target.:Attribute Information (in order):- CRIM     per capita crime rate by town- ZN       proportion of residential land zoned for lots over 25,000 sq.ft.- INDUS    proportion of non-retail business acres per town- CHAS     Charles River dummy variable (= 1 if tract bounds river; 0 otherwise)- NOX      nitric oxides concentration (parts per 10 million)- RM       average number of rooms per dwelling- AGE      proportion of owner-occupied units built prior to 1940- DIS      weighted distances to five Boston employment centres- RAD      index of accessibility to radial highways- TAX      full-value property-tax rate per $10,000- PTRATIO  pupil-teacher ratio by town- B        1000(Bk - 0.63)^2 where Bk is the proportion of black people by town- LSTAT    % lower status of the population- MEDV     Median value of owner-occupied homes in $1000's:Missing Attribute Values: None:Creator: Harrison, D. and Rubinfeld, D.L.This is a copy of UCI ML housing dataset.
https://archive.ics.uci.edu/ml/machine-learning-databases/housing/This dataset was taken from the StatLib library which is maintained at Carnegie Mellon University.
The Boston house-price data of Harrison, D. and Rubinfeld, D.L. 'Hedonic
prices and the demand for clean air', J. Environ. Economics & Management,
vol.5, 81-102, 1978.   Used in Belsley, Kuh & Welsch, 'Regression diagnostics
...', Wiley, 1980.   N.B. Various transformations are used in the table on
pages 244-261 of the latter.The Boston house-price data has been used in many machine learning papers that address regression
problems.   .. topic:: References- Belsley, Kuh & Welsch, 'Regression diagnostics: Identifying Influential Data and Sources of Collinearity', Wiley, 1980. 244-261.- Quinlan,R. (1993). Combining Instance-Based and Model-Based Learning. In Proceedings on the Tenth International Conference of Machine Learning, 236-243, University of Massachusetts, Amherst. Morgan Kaufmann.

波士顿房价数据集的特征共有14种，分别是CRIM（城镇人均犯罪率）、ZN（占地面积超过25000平方英尺的住宅用地比例）、INDUS（非零售商业用地占比）、CHAS（是否临河）、NOX（氮氧化物浓度）、RM（房屋房间数）、AGE（房屋年龄）、DIS（和就业中心的距离）、RAD（是否容易上高速路）、TAX（税率）、PTRATTO（学生人数比老师人数）、B（城镇黑人比例计算的统计值）、LSTAT（低收入人群比例）和MEDV（房价中位数）。原文链接：https://blog.csdn.net/f18896984569/article/details/127759937。

这个数据下载到哪里了呢？我们可以通过打印boston获取位置信息（print(boston)),这里列出部分信息：位置在：D:\\pythonProject\\venv\\lib\\site-packages\\sklearn\\datasets\\data\\boston_house_prices.csv

 per $10,000\n        - PTRATIO  pupil-teacher ratio by town\n        - B        1000(Bk - 0.63)^2 where Bk is the proportion of black people by town\n        - LSTAT    % lower status of the population\n        - MEDV     Median value of owner-occupied homes in $1000's\n\n    :Missing Attribute Values: None\n\n    :Creator: Harrison, D. and Rubinfeld, D.L.\n\nThis is a copy of UCI ML housing dataset.\nhttps://archive.ics.uci.edu/ml/machine-learning-databases/housing/\n\n\nThis dataset was taken from the StatLib library which is maintained at Carnegie Mellon University.\n\nThe Boston house-price data of Harrison, D. and Rubinfeld, D.L. 'Hedonic\nprices and the demand for clean air', J. Environ. Economics & Management,\nvol.5, 81-102, 1978.   Used in Belsley, Kuh & Welsch, 'Regression diagnostics\n...', Wiley, 1980.   N.B. Various transformations are used in the table on\npages 244-261 of the latter.\n\nThe Boston house-price data has been used in many machine learning papers that address regression\nproblems.   \n     \n.. topic:: References\n\n   - Belsley, Kuh & Welsch, 'Regression diagnostics: Identifying Influential Data and Sources of Collinearity', Wiley, 1980. 244-261.\n   - Quinlan,R. (1993). Combining Instance-Based and Model-Based Learning. In Proceedings on the Tenth International Conference of Machine Learning, 236-243, University of Massachusetts, Amherst. Morgan Kaufmann.\n", 'filename': 'D:\\pythonProject\\venv\\lib\\site-packages\\sklearn\\datasets\\data\\boston_house_prices.csv'}Process finished with exit code 0

我们打开路径可以看到：

显示时间不是当前时间，说明之前已经下载过。

打开数据如下，显示前面11行：

第一行显示数据有506行记录，13个变量，最后一列为房价中位数。我们将第一行删除掉便于数据操作。把文件复制到当前路径下与操作，另存为一份Excel格式。

excel文件读取

def read_excel(io: {engine, parse},sheet_name: int = 0,header: int = 0,names: Any = None,index_col: Any = None,usecols: Any = None,squeeze: bool = False,dtype: Any = None,engine: {__ne__} = None,converters: Any = None,true_values: Any = None,false_values: Any = None,skiprows: Any = None,nrows: Any = None,na_values: Any = None,keep_default_na: bool = True,na_filter: bool = True,verbose: bool = False,parse_dates: bool = False,date_parser: Any = None,thousands: Any = None,comment: Any = None,skipfooter: int = 0,convert_float: bool = True,mangle_dupe_cols: bool = True,storage_options: Optional[Dict[str, Any]] = None)

示例：读取excel文件数据，默认读取所有数据：

df=pd.read_excel('boston_house_prices.xls')
print(df)

csv文件读取

read_csv函数中参数更多：

def read_csv(filepath_or_buffer: PathLike[str],sep: Any = lib.no_default,delimiter: Any = None,header: str = "infer",names: Any = None,index_col: Any = None,usecols: Any = None,squeeze: bool = False,prefix: Any = None,mangle_dupe_cols: bool = True,dtype: Any = None,engine: Any = None,converters: Any = None,true_values: Any = None,false_values: Any = None,skipinitialspace: bool = False,skiprows: Any = None,skipfooter: int = 0,nrows: Any = None,na_values: Any = None,keep_default_na: bool = True,na_filter: bool = True,verbose: bool = False,skip_blank_lines: bool = True,parse_dates: bool = False,infer_datetime_format: bool = False,keep_date_col: bool = False,date_parser: Any = None,dayfirst: bool = False,cache_dates: bool = True,iterator: bool = False,chunksize: Any = None,compression: str = "infer",thousands: Any = None,decimal: str = ".",lineterminator: Any = None,quotechar: str = '\"',quoting: int = csv.QUOTE_MINIMAL,doublequote: bool = True,escapechar: Any = None,comment: Any = None,encoding: Any = None,dialect: Any = None,error_bad_lines: bool = True,warn_bad_lines: bool = True,delim_whitespace: bool = False,low_memory: Optional[bool] = _c_parser_defaults["low_memory"],memory_map: bool = False,float_precision: Any = None,storage_options: Optional[Dict[str, Any]] = None)

示例：读取csv数据，默认读取前5行：

df = pd.read_csv(# 该参数为数据在电脑中的路径，可以不填写filepath_or_buffer='boston_house_prices.csv',# 该参数代表数据的分隔符，csv文件默认是逗号。其他常见的是'\t'sep=',',# 该参数代表跳过数据文件的的第1行不读入# skiprows=1,# nrows，只读取前n行数据，若不指定，读入全部的数据nrows=5,
)

2.数据保存

excel文件保存,需要import xlwt

df.to_excel('boston_part.xls')

csv文件保存

df.to_csv('boston_part.csv')

3.数据指定位置读取与切片

可通过iloc方法来实现

newdf=df.iloc[:,:] ，索引从0开始

示例：读取指定位置数据，比如第5行第5列数据

df = pd.read_csv('boston_house_prices.csv')
df=df.iloc[4,4]

读取5行5列数据：

df = pd.read_csv('boston_house_prices.csv')
df=df.iloc[:5,:5]
print(df)

结果如下：

      CRIM    ZN  INDUS  CHAS    NOX
0  0.00632  18.0   2.31     0  0.538
1  0.02731   0.0   7.07     0  0.469
2  0.02729   0.0   7.07     0  0.469
3  0.03237   0.0   2.18     0  0.458
4  0.06905   0.0   2.18     0  0.458

读取指定位置5行数据所有列：

df = pd.read_csv('boston_house_prices.csv')
df=df.iloc[10:15,:]
print(df)

运行结果：

       CRIM    ZN  INDUS  CHAS    NOX  ...  TAX  PTRATIO       B  LSTAT  MEDV
10  0.22489  12.5   7.87     0  0.524  ...  311     15.2  392.52  20.45  15.0
11  0.11747  12.5   7.87     0  0.524  ...  311     15.2  396.90  13.27  18.9
12  0.09378  12.5   7.87     0  0.524  ...  311     15.2  390.50  15.71  21.7
13  0.62976   0.0   8.14     0  0.538  ...  307     21.0  396.90   8.26  20.4
14  0.63796   0.0   8.14     0  0.538  ...  307     21.0  380.02  10.26  18.2

同样的，读取指定列所有行也是一样的。

4.数据合并连接

pd.concat([df1,df2],axis=1) 横向合并数据

df = pd.read_csv('boston_house_prices.csv')
df1=df.iloc[:,:13]
df2=df.iloc[:,13]
print(df1,df2)
df3=pd.concat([df1,df2],axis=1)
print(df3)

纵向合并数据：

df = pd.read_csv('boston_house_prices.csv')
df1=df.iloc[:5,:]
df2=df.iloc[5:10,:]
print(df1,df2)
df3=pd.concat([df1,df2],axis=0)
print(df3)

5.根据条件读取数据

只选择中位数房价大于30的数据。df['MEDV']>30

df = pd.read_csv('boston_house_prices.csv')
df=df[df['MEDV']>30]
print(df)

6.根据条件删除数据

删除房价大于30的数据：

indexname=df[df['MEDV']>30].index
df.drop(index,Inplace=True)

7.统计函数

df = pd.read_csv('boston_house_prices.csv')
print(df['MEDV'].mean())  # 求一整列的均值，返回一个数。会自动排除空值。
print(df[['MEDV', 'LSTAT']].mean())  # 求两列的均值，返回两个数，Series
print(df[['MEDV', 'LSTAT']])
print(df[['MEDV', 'LSTAT']].mean(axis=1))  # 求两列的均值，返回DataFrame。axis=0或者1要搞清楚。
#axis=1，代表对整几列进行操作。axis=0（默认）代表对几行进行操作。实际中弄混很正常，到时候试一下就知道了。
print(df['MEDV'].max())  # 最大值
print(df['MEDV'].min())  # 最小值
print(df['MEDV'].std())  # 标准差
print(df['MEDV'].count())  # 非空的数据的数量
print(df['MEDV'].median())  # 中位数
print(df['MEDV'].quantile(0.25))  # 25%分位数

后续将继续更新完善！