这是我的barplot外观的一个简单示例：
x <- data.frame(aa=c(0.2,0.6,0.1), dd = c(1,2,3))
x <- melt(x, "dd")
y <- data.frame(bb=c(0.4,0.5), dd = c(1,2))
y <- melt(y, "dd")
z <- data.frame(cc=c(0.5,0.25,0.1,0.05), dd = c(1,2,3,4))
z <- melt(z, "dd")
x=rbind(x,y,z)
col=c("white","grey","blue","white","red","white","green","blue","green")
ggplot(x, aes(x = variable, y = value)) + geom_bar(stat = "identity", fill = col)
我想知道是否有一种方法可以使我的条形圆角末端变圆，例如使用lineline选项（http://sape.inf.usi.ch/quick-reference/ggplot2/lineend）？