最近新手接触 R 语言，在做一道练习的时候，利用plot()进行画折线图，在最后一步调用legend() 添加图例的时候，死活都没有产生出来。
直接贴出 脚本
library("quantmod")
symbols=c('^VLIC','GE','KO','AAPL','MCD')
getSymbols(symbols,src='yahoo',from="2012-02-01",to="2013-02-01")
#obtain adjusted closed
VLICad = VLIC$VLIC.Adjusted
GEad= GE$GE.Adjusted
KOad=KO$KO.Adjusted
AAPLad=AAPL$AAPL.Adjusted
MCDad = MCD$MCD.Adjusted
#compute cumulative sum (cumsum) of daily returns (Delt)
#Remove first term of the series, with [-1,], since cumsum is not defined for it.
vl = cumsum((Delt(VLICad)*100)[-1,])
ge = cumsum((Delt(GEad)*100)[-1,])
ko = cumsum((Delt(KOad)*100)[-1,])
ap = cumsum((Delt(AAPLad)*100)[-1,])
md = cumsum((Delt(MCDad)*100)[-1,])
###range of values for the plot
lim = c(min(vl,ge,ko,ap,md),max(vl,ge,ko,ap,md))
plot(vl,main="",ylim=lim,xlab="dates",ylab="% benefits")
lines(ge,col="green")
lines(ko,col="red")
lines(ap,col="violet")
lines(md,col="yellow")
## THE FOLLOWING SCRIPT DOES NOT WORK!!!
legend("topright",c("VLIC","GE","KO","AAPL","MCD"),col=c("black","green","red","violet","yellow"),text.col=c("black","green","red","violet","yellow"))
最后生成出来的是
result.png
于是乎，R 可以查看帮助, 输入这个脚本执行，会弹出页面帮助
?legend
弹出的页面
?legend
页面介绍了这个方法，具体参数说明，以及使用实例。
开始一看，十多个参数。。。有点慌，还好不是每个都要用。
前后对比，没有毛病啊！！！ 就是不出来图例...
网上搜。。。没有找到解决办法~
查看别人家的demo，可是很顺利出来。
别人家的demo
模仿别人的来写，还是不行，简直要崩溃...
最后在网上发帖子求教，最后有@Dan Y 大牛给出了答案：
Because vl has class xts, when you call the generic function plot, the method plot.xts is dispatched. legend doesn't play very nicely with xts plots, but xts::addLegend does.
言下之意，就是legend() 支持不是那么好，可以使用xts的addLegend()方法替换。在他的提示下执行如下脚本：
colvec <- c("black","green","red","violet","yellow")
xts::addLegend(legend.loc="topleft", legend.names=c("VLIC","GE","KO","AAPL","MCD"),lty = 1, col=colvec, text.col=colvec, bg="white", bty=1)
# 直接如下代码也行
# addLegend(legend.loc="topright", legend.names=c("VLIC","GE","KO","AAPL","MCD"),lty = 1, col=colvec, text.col=colvec, bg="white", bty=1)
最后结果
终于成功
参考资料
