python数据分析(pandas入门)
2021/7/1 22:24:08
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1、pandas数据结构之DataFrame
DataFrame生成方式:1、从另一个DataFrame创建。2、从具有二维形状的NumPy数组或数组的复合结构生成。3、使用Series创建。4、从CSV之类文件生成。下面介绍DataFrame的简单用法:
a):读取文件
代码:
from pandas.io.parsers import read_csv df=read_csv("H:\Python\data\WHO.csv") print "DataFrame:",df [/code] 运行结果(只截取部分): ```code DataFrame: Country CountryID Continent \ Afghanistan 1 1 Albania 2 2 Algeria 3 3 Andorra 4 2 Angola 5 3
b):得到形状数据
代码:
print "Shape:",df.shape #大小 print "Length:",len(df) #长度 [/code] 结果: ```code Shape: (202, 358) Length: 202 [/code] c):得到列标题及类型数据 代码: ```code print "Column Headers",df.columns #得到每列的标题 print "Data type",df.dtypes #得到每列数据的类型 [/code] 结果(截取部分) ```code Column Headers Index([u'Country', u'CountryID', u'Continent', u'Adolescent fertility rate (%)', u'Adult literacy rate (%)', u'Gross national income per capita (PPP international $)', u'Net primary school enrolment ratio female (%)', u'Net primary school enrolment ratio male (%)', u'Population (in thousands) total', u'Population annual growth rate (%)', ... u'Total_CO2_emissions', u'Total_income', u'Total_reserves', u'Trade_balance_goods_and_services', u'Under_five_mortality_from_CME', u'Under_five_mortality_from_IHME', u'Under_five_mortality_rate', u'Urban_population', u'Urban_population_growth', u'Urban_population_pct_of_total'], dtype='object', length=358) Data type Country object CountryID int64 Continent int64 Adolescent fertility rate (%) float64 Adult literacy rate (%) float64 Gross national income per capita (PPP international $) float64 Net primary school enrolment ratio female (%) float64 Net primary school enrolment ratio male (%) float64
d):索引
代码:
print "Index:",df.index [/code] 结果: ```code Index: RangeIndex(start=0, stop=202, step=1) [/code] e):values,非数值数据标位nan 代码: ```code print "Vales:",df.values [/code] 结果 ```code Vales: [['Afghanistan' 1L 1L ..., 5740436.0 5.44 22.9] ['Albania' 2L 2L ..., 1431793.9 2.21 45.4] ['Algeria' 3L 3L ..., 20800000.0 2.61 63.3] ..., ['Yemen' 200L 1L ..., 5759120.5 4.37 27.3] ['Zambia' 201L 3L ..., 4017411.0 1.95 35.0] ['Zimbabwe' 202L 3L ..., 4709965.0 1.9 35.9]] [/code] ## 2、pandas数据结构之Series pandas的Series数据结构是由不同类型的元素组成的一维数组,该数据结构也具有标签,创建方式有:由Python字典创建;由numpy数组创建;由单个标量值创建。 a):类型。当选中DataFrame的一列时,得到的是一个Series型的数据。 代码: ```code country_df=df["Country"] print "Type df:",type(df) print "Type country_df:",type(country_df) [/code] 结果: ```code Type df: <class 'pandas.core.frame.DataFrame'> Type country_df: <class 'pandas.core.series.Series'> [/code] b):属性。pandas的Series数据结构不仅共享了DataFrame的一些属性,还提供与名称相关的一个属性。 代码: ```code print "Series Shape:",country_df.shape #获取列的形状 print "Series index:",country_df.index #获取索引 print "Series values:",country_df.values #获取该列的所有值 print "Series name:",country_df.name #获取列名(标题) [/code] 结果: ```code Series Shape: (202L,) Series index: RangeIndex(start=0, stop=202, step=1) Series values: ['Afghanistan' 'Albania' 'Algeria' 'Andorra' 'Angola' 'Antigua and Barbuda' 'Argentina' 'Armenia' 'Australia' 'Austria' 'Azerbaijan' 'Bahamas' 'Bahrain' 'Bangladesh' 'Barbados' 'Belarus' 'Belgium' 'Belize' 'Benin' 'Bermuda' 'Bhutan' 'Bolivia' 'Bosnia and Herzegovina' 'Botswana' 'Brazil' 'Brunei Darussalam' 'Bulgaria' 'Burkina Faso' 'Burundi' 'Cambodia' 'Cameroon' 'Canada' 'Cape Verde' 'Central African Republic' 'Chad' 'Chile' 'China' 'Colombia' 'Comoros' 'Congo, Dem. Rep.' 'Congo, Rep.' 'Cook Islands' 'Costa Rica' "Cote d'Ivoire" 'Croatia' 'Cuba' 'Cyprus' 'Czech Republic' 'Denmark' 'Djibouti' 'Dominica' 'Dominican Republic' 'Ecuador' 'Egypt' 'El Salvador' 'Equatorial Guinea' 'Eritrea' 'Estonia' 'Ethiopia' 'Fiji' 'Finland' 'France' 'French Polynesia' 'Gabon' 'Gambia' 'Georgia' 'Germany' 'Ghana' 'Greece' 'Grenada' 'Guatemala' 'Guinea' 'Guinea-Bissau' 'Guyana' 'Haiti' 'Honduras' 'Hong Kong, China' 'Hungary' 'Iceland' 'India' 'Indonesia' 'Iran (Islamic Republic of)' 'Iraq' 'Ireland' 'Israel' 'Italy' 'Jamaica' 'Japan' 'Jordan' 'Kazakhstan' 'Kenya' 'Kiribati' 'Korea, Dem. Rep.' 'Korea, Rep.' 'Kuwait' 'Kyrgyzstan' "Lao People's Democratic Republic" 'Latvia' 'Lebanon' 'Lesotho' 'Liberia' 'Libyan Arab Jamahiriya' 'Lithuania' 'Luxembourg' 'Macao, China' 'Macedonia' 'Madagascar' 'Malawi' 'Malaysia' 'Maldives' 'Mali' 'Malta' 'Marshall Islands' 'Mauritania' 'Mauritius' 'Mexico' 'Micronesia (Federated States of)' 'Moldova' 'Monaco' 'Mongolia' 'Montenegro' 'Morocco' 'Mozambique' 'Myanmar' 'Namibia' 'Nauru' 'Nepal' 'Netherlands' 'Netherlands Antilles' 'New Caledonia' 'New Zealand' 'Nicaragua' 'Niger' 'Nigeria' 'Niue' 'Norway' 'Oman' 'Pakistan' 'Palau' 'Panama' 'Papua New Guinea' 'Paraguay' 'Peru' 'Philippines' 'Poland' 'Portugal' 'Puerto Rico' 'Qatar' 'Romania' 'Russia' 'Rwanda' 'Saint Kitts and Nevis' 'Saint Lucia' 'Saint Vincent and the Grenadines' 'Samoa' 'San Marino' 'Sao Tome and Principe' 'Saudi Arabia' 'Senegal' 'Serbia' 'Seychelles' 'Sierra Leone' 'Singapore' 'Slovakia' 'Slovenia' 'Solomon Islands' 'Somalia' 'South Africa' 'Spain' 'Sri Lanka' 'Sudan' 'Suriname' 'Swaziland' 'Sweden' 'Switzerland' 'Syria' 'Taiwan' 'Tajikistan' 'Tanzania' 'Thailand' 'Timor-Leste' 'Togo' 'Tonga' 'Trinidad and Tobago' 'Tunisia' 'Turkey' 'Turkmenistan' 'Tuvalu' 'Uganda' 'Ukraine' 'United Arab Emirates' 'United Kingdom' 'United States of America' 'Uruguay' 'Uzbekistan' 'Vanuatu' 'Venezuela' 'Vietnam' 'West Bank and Gaza' 'Yemen' 'Zambia' 'Zimbabwe'] Series name: Country [/code] c):切片。 代码: ```code print "Last 2 countries:",country_df[-2:] print "Last 2 countries type:",type(country_df[-2:]) [/code] 结果: ```code Last 2 countries: 200 Zambia Zimbabwe Name: Country, dtype: object Last 2 countries type: <class 'pandas.core.series.Series'> [/code] ## 3、利用Pandas查询数据 a):head()和tail()函数: 代码: ```code sunspots=read_csv("H:\Python\data\sunspots.csv") print "Head 2:",sunspots.head(2) #查看前两行 print "Tail 2:",sunspots.tail(2) #查看后两行 [/code] 运行结果: ```code Head 2: Date Yearly Mean Total Sunspot Number 2016/12/31 39.8 2015/12/31 69.8 Tail 2: Date Yearly Mean Total Sunspot Number 1701-12-31 18.3 1700-12-31 8.3 [/code] b):loc函数 代码: ```code last_date=sunspots.index[-1] print "Last value:\n",sunspots.loc[last_date] [/code] 运行结果: ```code last_date=sunspots.index[-1] print "Last value:\n",sunspots.loc[last_date] [/code] ## 4、利用Pandas的DataFrame进行统计计算 pandas的DataFrame数据结构为我们提供了若干统计函数,下面给出部分方法及其简要说明。 方法 | 说明 ---|--- describe | 这个方法返回描述性统计信息 count | 返回非NAN数据项的数量 mad | 计算平均绝对偏差,级类似于标准差的一个有力统计工具 median | 返回中位数,等价于第50百分位数的值 min | 返回最小值 max | 返回最大值 mode | 返回众数(mod),即一组数据中出现次数最多的变量值 std | 返回表示离散度的标准差,即方差的平方根 var | 返回方差 skew | 返回偏差系数(skewness),该系数表示的是数据分布的对称程度 kurt | 这个方法将返回峰太系数,反映数据分布曲线顶端尖峭或扁平程度 代码: ```code print "Describe:\n",sunspots.describe() print "Non NaN observations:\n",sunspots.count() print "MAD:\n",sunspots.mad() print "Median:\n",sunspots.median() print "Min:\n",sunspots.min() print "Max:\n",sunspots.max() print "Mode:\n",sunspots.mode() print "Standard Deviation:\n",sunspots.std() print "Variance:\n",sunspots.var() print "Skewness:\n",sunspots.skew() print "Kurtosis:\n",sunspots.kurt()
运行结果:
Describe: Yearly Mean Total Sunspot Number count 318.000000 mean 79.193396 std 61.988788 min 0.000000 25% 24.950000 50% 66.250000 75% 116.025000 max 269.300000 Non NaN observations: Date 318 Yearly Mean Total Sunspot Number 318 dtype: int64 MAD: Yearly Mean Total Sunspot Number 50.925104 dtype: float64 Median: Yearly Mean Total Sunspot Number 66.25 dtype: float64 Min: Date 1700-12-31 Yearly Mean Total Sunspot Number 0 dtype: object Max: Date 2016/12/31 Yearly Mean Total Sunspot Number 269.3 dtype: object Mode: Date Yearly Mean Total Sunspot Number 1985/12/31 18.3 Standard Deviation: Yearly Mean Total Sunspot Number 61.988788 dtype: float64 Variance: Yearly Mean Total Sunspot Number 3842.60983 dtype: float64 Skewness: Yearly Mean Total Sunspot Number 0.808551 dtype: float64 Kurtosis: Yearly Mean Total Sunspot Number -0.130045 dtype: float64 [/code] ## 5、利用pandas的DataFrame实现数据聚合 a):为numpy的随机数生成器指定种子,以确保重复运行程序时生成的数据不会走样。该数据有4列: 1、Weather(一个字符串); 2、Food(一个字符串); 3、Price(一个随机浮点数); 4、Number(1~9之间的一个随机整数)。 代码: ```code import pandas as pd from numpy.random import seed from numpy.random import rand from numpy.random import randint import numpy as np seed(42) #random.rand(n),生成n个0到1间随机数 #random.random_integers(low,high=None,size=None) 生成闭区间[low,high]上离散均匀分布的整数值;若high=None,则取值区间变为[1,low] df=pd.DataFrame({'Weather':['cold','hot','cold','hot','cold','hot','cold'],'Food':['soup','soup','icecream','chocolate','icecream','icecream','soup'], 'Price':10*rand(7),'Number':randint(1,9,size=(7,))}) print df [/code] 运行结果: ```code Food Number Price Weather soup 8 3.745401 cold soup 5 9.507143 hot icecream 4 7.319939 cold chocolate 8 5.986585 hot icecream 8 1.560186 cold icecream 3 1.559945 hot soup 6 0.580836 cold
b):通过Weather列为数据分组,然后遍历各组数据
代码:
weather_group=df.groupby('Weather') #按天气分组 i=0 for name,group in weather_group: i=i+1 print "Group ",i,name print group [/code] 运行结果: ```code Group 1 cold Food Number Price Weather soup 8 3.745401 cold icecream 4 7.319939 cold icecream 8 1.560186 cold soup 6 0.580836 cold Group 2 hot Food Number Price Weather soup 5 9.507143 hot chocolate 8 5.986585 hot icecream 3 1.559945 hot [/code] c):变量Weather_group是一种特殊的pandas对象,可由groupby()生成。这个对象为我们提供了聚合函数,下面展示它的用法: 代码: ```code print "Weather group first:\n",weather_group.first() #展示各组第一行内容 print "Weather group last:\n",weather_group.last() #展示各组最后一行内容 print "Weather group mean:\n",weather_group.mean() #计算各组均值 [/code] 运行结果: ```code Weather group first: Food Number Price Weather cold soup 8 3.745401 hot soup 5 9.507143 Weather group last: Food Number Price Weather cold soup 6 0.580836 hot icecream 3 1.559945 Weather group mean: Number Price Weather cold 6.500000 3.301591 hot 5.333333 5.684558
d):恰如利用数据库的查询操作那样,也可以针对多列进行分组。
然后就可以用groups属性来了解所生成的数据组,以及每一组包含的行数:
代码:
wf_group=df.groupby(['Weather','Food']) print "WF Group:\n",wf_group.groups [/code] 运行结果: ```code WF Group: {('hot', 'chocolate'): Int64Index([3], dtype='int64'), ('cold', 'icecream'): Int64Index([2, 4], dtype='int64'), ('cold', 'soup'): Int64Index([0, 6], dtype='int64'), ('hot', 'soup'): Int64Index([1], dtype='int64'), ('hot', 'icecream'): Int64Index([5], dtype='int64')}
e):通过agg方法,可以对数据组施加一系列的numpy函数:
代码:
print "WF Aggregated:\n",wf_group.agg([np.mean,np.median]) [/code] 运行结果: ```code WF Aggregated: Number Price mean median mean median Weather Food cold icecream 6 6 4.440063 4.440063 soup 7 7 2.163119 2.163119 hot chocolate 8 8 5.986585 5.986585 icecream 3 3 1.559945 1.559945 soup 5 5 9.507143 9.507143
6、DataFrame的串联与附加操作
a):数据库中的数据表有内部连接与外部连接两种连接类型。pandas的DataFrame也有类似操作,也可以对数据进行串联和附加。
函数concat()的作用是串联DataFrame,如可以把一个由3行数据组成的DataFrame与其他行数据行串接,以便重建原DataFrame:
代码:
print "df:3\n",df[:3] print "Contact Back together:\n",pd.concat([df[:3],df[:3]]) [/code] 运行结果: ```code df:3 Food Number Price Weather soup 8 3.745401 cold soup 5 9.507143 hot icecream 4 7.319939 cold Contact Back together: Food Number Price Weather soup 8 3.745401 cold soup 5 9.507143 hot icecream 4 7.319939 cold soup 8 3.745401 cold soup 5 9.507143 hot icecream 4 7.319939 cold
b):为了追加数据行,可以使用append函数:
代码:
print "Appending rows:\n",df[3:].append(df[5:]) [/code] 运行结果: ```code Appending rows: Food Number Price Weather 3 chocolate 8 5.986585 hot 4 icecream 8 1.560186 cold 5 icecream 3 1.559945 hot 6 soup 6 0.580836 cold 5 icecream 3 1.559945 hot 6 soup 6 0.580836 cold [/code] 7、连接DataFrames a)、新建两个CSV文件:dest.csv和tips.csv 代码: ```code dests=pd.read_csv("H:\Python\data\dest.csv") tips=pd.read_csv("H:\Python\data\\tips.csv") print "dests:\n",dests print "tips:\n",tips [/code] 运行结果: ```code dests: EmpNr Dest 0 5 The Hague 1 3 Amsterdam 2 9 Rotterdam tips: EmpNr Amount 0 5 10.0 1 9 5.0 2 7 2.5 [/code] b):pandas提供的merge函数或DataFrame的join函数实例方法都能实现类似数据库的连接操作数功能。 pandas支持所有的这些连接类型,这里仅介绍内部连接与完全外部连接。 * 用merge函数按照员工编号进行连接处理,代码如下: ```code print "Merge() on key:\n",pd.merge(dests,tips,on='EmpNr') [/code] 运行结果: ```code Merge() on key: EmpNr Dest Amount 0 5 The Hague 10.0 1 9 Rotterdam 5.0
-
使用join方法执行连接操作,需要使用后缀来指示左操作对象和右操作对象:
print "Dest join() tips:\n",dests.join(tips,lsuffix='Dest',rsuffix='Tips') [/code] 运行结果: ```code Dest join() tips: EmpNrDest Dest EmpNrTips Amount 0 5 The Hague 5 10.0 1 3 Amsterdam 9 5.0 2 9 Rotterdam 7 2.5 [/code] * 用merge()执行内部连接和外部连接时,更显示的方法如下所示: 代码: ```code print "Inner join with merge():\n",pd.merge(dests,tips,how='inner') #内连接 print "Outer join with merge():\n",pd.merge(dests,tips,how='outer') #完全外部连接 [/code] 运行结果: ```code Inner join with merge(): EmpNr Dest Amount 0 5 The Hague 10.0 1 9 Rotterdam 5.0 Outer join with merge(): EmpNr Dest Amount 0 5 The Hague 10.0 1 3 Amsterdam NaN 2 9 Rotterdam 5.0 3 7 NaN 2.5 [/code] ## 8、处理缺失数据 a):读取数据。 代码: ```code df=pd.read_csv("H:\Python\data\WHO.csv") #print df.head() df=df[['Country',df.columns[6]]][:2] #将原df的Country列和第6列组成新DataFrame,并取前两行 print "New df:\n",df [/code] 运行结果: ```code New df: Country Net primary school enrolment ratio female (%) 0 Afghanistan NaN 1 Albania 93.0
b):pandas会把缺失的数值标记为NaN,表示None。pandas的isnull()函数可以帮我们检查缺失的数据。
代码:
print "Null Values:\n",pd.isnull(df) #检查每行缺失的数 print "Not Null Values:\n",pd.notnull(df) #检查非缺失的数 print "Last Column Doubled:\n",2*df[df.columns[-1]] #NAN值乘以一个数后还是NAN print "Last Column plus NaN:\n",df[df.columns[-1]]+np.nan #非NAN值加上NAN后变为了NAN print "Zero filled:\n",df.fillna(0) #使用0替换NAN
运行结果:
Null Values: Country Net primary school enrolment ratio female (%) 0 False True 1 False False Not Null Values: Country Net primary school enrolment ratio female (%) 0 True False 1 True True Last Column Doubled: 0 NaN 1 186.0 Name: Net primary school enrolment ratio female (%), dtype: float64 Last Column plus NaN: 0 NaN 1 NaN Name: Net primary school enrolment ratio female (%), dtype: float64 Zero filled: Country Net primary school enrolment ratio female (%) 0 Afghanistan 0.0 1 Albania 93.0 [/code] ## 9、处理日期数据 a):设定从1900年1月1日开始为期42天的时间范围。 代码: ```code print "Date range:\n",pd.date_range('1/1/1900',periods=42,freq='D') #42表示天数,D表示使用日频率。如果periods='W',表示42周 [/code] 运行结果: ```code Date range: DatetimeIndex(['1900-01-07', '1900-01-14', '1900-01-21', '1900-01-28', '1900-02-04', '1900-02-11', '1900-02-18', '1900-02-25', '1900-03-04', '1900-03-11', '1900-03-18', '1900-03-25', '1900-04-01', '1900-04-08', '1900-04-15', '1900-04-22', '1900-04-29', '1900-05-06', '1900-05-13', '1900-05-20', '1900-05-27', '1900-06-03', '1900-06-10', '1900-06-17', '1900-06-24', '1900-07-01', '1900-07-08', '1900-07-15', '1900-07-22', '1900-07-29', '1900-08-05', '1900-08-12', '1900-08-19', '1900-08-26', '1900-09-02', '1900-09-09', '1900-09-16', '1900-09-23', '1900-09-30', '1900-10-07', '1900-10-14', '1900-10-21'], dtype='datetime64[ns]', freq='W-SUN')
b):在pandas中,日期区间是有限制的。pandas的时间戳基于numpy datetime64类型,以纳秒为单位,并且用一个64位整数来表示具体数值。因此,日期有效的时间戳介于1677年至2262年。当然,这些年份也不是所有日期都是有效的。这个时间范围的精确中点是1970年1月1日。这样,1677年1月1日就无法用pandas时间戳定义,而1677年9月30日就可以,下面用代码说明:
代码:
import pandas as pd import sys try: print "Date range:\n",pd.date_range('1/1/1677',periods=4,frep='D') except: etype,value,_=sys.exc_info() #获得错误类型,错误值 print "Error encountered:\n",etype,value #打印 [/code] 运行结果: ```code Date range: Error encountered: <class 'pandas.tslib.OutOfBoundsDatetime'> Out of bounds nanosecond timestamp: 1677-01-01 00:00:00
b):使用pandas的Dateoffset函数计算允许的日期范围:
代码:
offset=pd.DateOffset(seconds=2**63/10**9) mid=pd.to_datetime('1/1/1970') print "Start valid range:\n",mid-offset print "End valid range:\n",mid+offset [/code] 运行结果: ```code Start valid range: 1677-09-21 00:12:44 End valid range: 2262-04-11 23:47:16 [/code] c):pandas可以把一串字符串转化成日期数据: 代码: ```code print "With format:\n",pd.to_datetime(['1901113','19031230'],format='%Y%m%d') [/code] 运行结果: ```code With format: DatetimeIndex(['1901-11-03', '1903-12-30'], dtype='datetime64[ns]', freq=None)
d):如果一个字符串明显不是日期,无法转化。可以使用参数coerce设置为True强制转化:
代码:
print "Illegal date:\n",pd.to_datetime(['1901-11-13','not a date']) #第二个字符串无法转换,运行报错 print "Illegal date:\n",pd.to_datetime(['1901-11-13','not a date'],coerce=True) #强制转化,得到非时间数NAT [/code] 运行结果: ```code Illegal date: DatetimeIndex(['1901-11-13', 'NaT'], dtype='datetime64[ns]', freq=None)
10、数据透析表
a):数据透析表可以从一个平面文件中指定的行和列中聚合数据,这种聚合操作可以是求和、求平均值,求标准差等运算。
import pandas as pd from numpy.random import seed from numpy.random import rand from numpy.random import randint import numpy as np seed(42) N=7 df=pd.DataFrame({'Weather':['cold','hot','cold','hot','cold','hot','cold'],'Food':['soup','soup','icecream','chocolate','icecream','icecream','soup'], 'Price':10*rand(7),'Number':randint(1,9,size=(7,))}) print "DataFrame:\n",df print pd.pivot_table(df,index='Food',aggfunc=np.sum) #计算各类型Food的统计值 [/code] 运行结果: ```code DataFrame: Food Number Price Weather 0 soup 8 3.745401 cold 1 soup 5 9.507143 hot 2 icecream 4 7.319939 cold 3 chocolate 8 5.986585 hot 4 icecream 8 1.560186 cold 5 icecream 3 1.559945 hot 6 soup 6 0.580836 cold Number Price Food chocolate 8 5.986585 icecream 15 10.440071 soup 19 13.833380
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