補(bǔ)充練習(xí)題

head(mtcars)

#先根據(jù)氣缸數(shù)正排序，再根據(jù)里程數(shù)逆排序

ordermtcars <- mtcars[order(mtcars$cyl,-mtcars$mpg),]
head(ordermtcars)

#用RODBC包從mangoTraining中連接外部數(shù)據(jù)Northwind.mdb文件中提取“Employees”，和“Orders"表格，合并
#這個(gè)找不到= =

library(mangoTraining)
if (!require(RODBC)) install.packages("RODBC")
library(RODBC)
system.file(package = "mangoTraining","extdata/NorthWind.mdb")

#使用reshape2包里面的tips數(shù)據(jù)計(jì)算性別和抽煙分類后給小費(fèi)的平均值

library(reshape2)
objects("package:reshape2")
tips <- reshape2::tips
head(tips)
nTips <- melt(tips,c("sex","smoker"),"tip")
head(nTips)
tipsMean <- dcast(nTips,.~sex+smoker,mean)
head(tipsMean)

#把djData中的Data列分為3個(gè)新列Month、Day、Year，確保不影響原始的Data
djData <- mangoTraining::dow_jones_data
library(lubridate)
head(djData)
djData$nDate <- as.character(djData$Date)
year<-strsplit(djData$nDate,split = "/")
year <- t(as.data.frame(year))
djData <- cbind(djData,year,row.names = rownames(djData))
colnames(djData)[c(9,10,11)] <- c("month","date","year")
head(djData)

一千個(gè)哈姆雷特，每道題都有不同的做法，做不出來就算了。
書已經(jīng)看了一大半了，思維貌似還沒有跟上，多練習(xí)。