ggplot2中的箭头标签方向

Question

我用这个 R 代码生成了双图：

set.seed(12345)
require(ggplot2)
AData <- data.frame(Glabel=LETTERS[1:7], A=rnorm(7, mean = 0, sd = 1), B=rnorm(7, mean = 0, sd = 1))
TData <- data.frame(Tlabel=LETTERS[11:20], A=rnorm(10, mean = 0, sd = 1), B=rnorm(10, mean = 0, sd = 1))
i <- 2
j <- 3
p <- ggplot(data=AData, aes(AData[, i], AData[, j])) + geom_point() + theme_bw()
p <- p + geom_text(aes(data=AData, label=Glabel), size=3, vjust=1.25, colour="black")
p <- p + geom_segment(data = TData, aes(xend = TData[ ,i], yend=TData[ ,j]),
              x=0, y=0, colour="black",
              arrow=arrow(angle=25, length=unit(0.25, "cm")))
p <- p + geom_text(data=TData, aes(x=TData[ ,i], y=TData[ ,j], label=Tlabel), size=3, vjust=1.35, colour="black")

输出

除了箭头标签之外，一切都很好。我希望标签位于箭头的末端，且方向与箭头相同。任何想法和/或解决方案。提前致谢。

Answer 1

两种可能性：

p <- p + geom_text(data=TData, aes(x=1.2*TData[ ,i], 
                                   y=1.2*TData[ ,j], 
                  label=Tlabel), size=3, vjust=0, colour="black")
p
#-----------------------------------
p <- p + geom_text(data=TData, aes(x=TData[ ,i] +.1*sign(TData[ ,i]), 
                                   y=TData[ ,j]+.1*sign(TData[ ,j]), 
                  label=Tlabel), size=3, vjust=0, colour="black")
p

第一种使标签与箭头的距离随“强度”而变化，而第二种在图形绘制比例上保持固定距离（可能是首选解决方案，如下所示）。

最后是一个完全“三角化”的版本，它将使标签与箭头完全相同。 （sign(.) 参数的相同性是反正切值约定的结果。Ya do what ya gatta do.）：

p <- ggplot(data=AData, aes(AData[, i], AData[, j])) + geom_point() + theme_bw()
p <- p + geom_text(aes(data=AData, label=Glabel), size=3, vjust=1.25, colour="black")
p <- p + geom_segment(data = TData, aes(xend = TData[ ,i], yend=TData[ ,j]),
              x=0, y=0, colour="black",
              arrow=arrow(angle=25, length=unit(0.25, "cm")))
p <- p + geom_text(data=TData, 
            aes(x=TData[ ,i] +.1*cos(atan(TData[ ,j]/TData[ ,i]))*sign(TData[ ,i]), 
                y=TData[ ,j] +.1*sin(atan(TData[ ,j]/TData[ ,i]))*sign(TData[ ,i]), 
            label=Tlabel), size=3, vjust=0, colour="red")

Answer 2

任何解决方案都可能需要一些手动定位。但最终在您的情况下，在不进行 vjust 调整的情况下绘制标签会更容易，然后稍微缩短每个箭头：

#This is the ad-hoc part to tinker with
l <- 1 - (0.05 * sqrt(1/with(TData,A^2 + B^2)))

p <- ggplot(data=AData, aes(AData[, i], AData[, j])) + geom_point() + theme_bw()
p <- p + geom_text(aes(data=AData, label=Glabel), size=3, vjust=1.25, colour="black")

#Scale the segments back slightly
p <- p + geom_segment(data = TData, aes(xend = TData[ ,i] * l, yend=TData[ ,j] * l),
              x=0, y=0, colour="black",
              arrow=arrow(angle=25, length=unit(0.25, "cm")))
p <- p + geom_text(data=TData, aes(x=TData[ ,i], y=TData[ ,j], label=Tlabel), size=3, colour="black")

由于箭头长度本身是固定的，因此线段的缩短必须与线段的长度成一定比例。

Answer 3

标签方向为箭头的更好解决方案：

set.seed(12345)
require(ggplot2)
AData <- data.frame(Glabel=LETTERS[1:7], A=rnorm(7, mean = 0, sd = 1), B=rnorm(7, mean = 0, sd = 1))
TData <- data.frame(Tlabel=LETTERS[11:20], A=rnorm(10, mean = 0, sd = 1), B=rnorm(10, mean = 0, sd = 1))
i <- 2
j <- 3
p <- ggplot(data=AData, aes(AData[, i], AData[, j])) + geom_point() + theme_bw()
p <- p + geom_text(aes(data=AData, label=Glabel), size=3, vjust=1.25, colour="black")

p <- p + geom_segment(data = TData, aes(xend = TData[ ,i], yend=TData[ ,j]),
              x=0, y=0, colour="black",
              arrow=arrow(angle=25, length=unit(0.25, "cm")))
p <- p + geom_text(
        data=TData
      , aes(x=TData[ ,i], y=TData[ ,j], label=Tlabel
            , angle = (180/pi) * atan(TData[ ,j]/TData[ ,i])
            , hjust = (1 - 2 * sign(TData[ ,i])) / 2)
      , size=3
      , colour="black")

print(p)