r shiny：动态编程图例位置

Question

在我的Shiny应用程序中，会生成堆积条形图。列数是可变的，取决于用户的输入。当列数很少时，图例会正确显示：

但是，当列数较高时，图例会重叠图表：

请你给我一个提示，告诉我如何动态编程图例的位置，以便它始终是1.可见; 2.与图表不重叠？谢谢！

以下是图表的代码：

par(mar=c(5,4,2,14)+1,xpd=TRUE,ps=14,cex.main=1.143,cex.lab=1.143,font.lab=2)
barplot(rbind(plotdffeedingh$apercentvector,plotdffeedingh$bpercentvector,plotdffeedingh$cpercentvector,plotdffeedingh$dpercentvector,plotdffeedingh$epercentvector,plotdffeedingh$fpercentvector),
        main="Feeding type composition of the herbivore nematode assemblage", xlim=c(0,length(plotdffeedingh$leveltreats)+2), 
        xlab="",ylab="Fraction, % of herbivore nematodes", names.arg=levels(plotdffeedingh$leveltreats), 
        legend.text=c("Sedentary parasites","Migratory endoparasites","Semi-endoparasites","Ectoparasites","Epidermal/root hair feeders","Algal/lichen/moss feeders"), 
        args.legend=list(x="right",inset=c(-0.2,0)),col=c("blue","yellow","red","grey","green","brown"),las=2)