1.在data.frame结构中，有时会有factor属性的值存在，不能直接使用as.numeric将factor中的数字直接转换，转换后的数据是错误的。一种方法是：使用as.character先将factor转换为character,再将character转换为numeric.
2.在R中设定横轴的时间刻度：
plot(x
<- sort(rnorm(47)), type = "s", main = "plot(x, type =
\"s\")", xaxt=‘n‘)
axis(1,c(0,10,20),c(‘01/10/23‘,‘10/12/06‘,‘11/03/18‘))
plot之后再使用axis增加，具体参考函数说明。
3.plot的说明，即legend，说明图中线的意义。
setwd("/Users/Yanyan/Documents/WorkDirectory/R Works/Coursera/Exploratory
Analysis/Project 1")
data <-
read.table(file="household_power_consumption.txt", header=TRUE,
sep=";")
handle <- subset(data, (as.Date(data$Date,format=‘%d/%m/%Y‘)
>= "2007-02-01") & (as.Date(data$Date,format=‘%d/%m/%Y‘) <=
"2007-02-02"))
png(filename="plot4.png", width=480, height=480,
units="px")
par(mfrow=c(2,2))
#Part
1
plot(as.numeric(as.character(handle$Global_active_power)),type="l",ylab="Global
Active Power",
xaxt=‘n‘,xlab="")
axis(1,c(0,length(handle$Global_active_power)/2,length(handle$Global_active_power)),c("Thu","Fri","Sat"))
##Part
2
plot(as.numeric(as.character(handle$Voltage)),type="l",ylab="Voltage",
xaxt=‘n‘,xlab="datetime")
axis(1,c(0,length(handle$Global_active_power)/2,length(handle$Global_active_power)),c("Thu","Fri","Sat"))
##Part
3
plot(as.numeric(as.character(handle$Sub_metering_1)),type="l",xaxt=‘n‘,yaxt=‘n‘,xlab="",ylab="Energy
sub metering")
lines(as.numeric(as.character(handle$Sub_metering_2)),
type="l",col="red")
lines(handle$Sub_metering_3,
type="l",col="blue")
axis(1,c(0,length(handle$Sub_metering_1)/2,length(handle$Sub_metering_1)),c("Thu","Fri","Sat"))
axis(side=2,at=seq(0,30,by=10))
legend("topright",
legend=c("Sub_metering_1","Sub_metering_2","Sub_metering_3"),col=c("black","red","blue"),lwd=1,lty=c(1,1,1),pch=c(NA,NA,NA))
##Part
4
plot(as.numeric(as.character(handle$Global_reactive_power)),type="l",ylab="Global_reactive_power",
xaxt=‘n‘,xlab="datetime")
axis(1,c(0,length(handle$Global_active_power)/2,length(handle$Global_active_power)),c("Thu","Fri","Sat"))
dev.off()
上述代码完全够了，不再赘述。
http://www.statmethods.net/advgraphs/layout.html