geom_segment箭头方向

Question

我正在尝试使用geom_segment绘制一些上下箭头。对于需要向上箭头和向下箭头的数据，我将数据集拆分为两部分。

但在这两个图上，箭头都是朝上的。这种情况如何才能逆转呢？有没有我遗漏的变量？

我使用的数据集如下所示：

GENE   START    END        STRAND
A      3000000  3000312    +
B      3001233  3090123    -

正链需要up-facing箭头，负链需要down-facing。

下面是我的代码：

# split the dataset in '+' and '-'
up.arrows <- genes.data[which(genes.data$STRAND=='+'),]
up.arrows.x <- runif(length(up.arrows$START), min = 0, max = length(up.arrows))

down.arrows <- genes.data[which(genes.data$STRAND=='-'),]
down.arrows.x <- runif(length(down.arrows$START), min = 0, max = length(down.arrows))

我使用runif，因为我不关心x-axis的位置。我主要关心的是y-axis。

ggplot(up.arrows, aes(up.arrows.x, up.arrows$START)) +
    geom_segment(aes(xend=up.arrows.x, yend=up.arrows$STOP), 
                 arrow = arrow(length = unit(0.1, "cm")),
                 colour = 'green4') + 
    geom_text_repel(size = 3,
                    aes(label = up.arrows$GENE),
                    color = 'black') +
    theme_classic(base_size = 16)

ggplot(down.arrows, aes(down.arrows.x, down.arrows$START)) +
    geom_segment(aes(xend=down.arrows.x, yend=down.arrows$STOP), 
                 arrow = arrow(length = unit(0.1, "cm")),
                 colour = 'green4') + 
    geom_text_repel(size = 3,
                    aes(label = down.arrows$GENE),
                    color = 'black',
                    segment.color = 'black') +
    theme_classic(base_size = 16)

之后，我想合并1ggplot中的点，因此区分up和down是很重要的

Answer 1

解决方案是一个小技巧。但我花了一些时间去思考。只需颠倒down-facing箭头的启动和停止。

而不是这样：

ggplot(down.arrows, aes(down.arrows.x, down.arrows$START)) +
    geom_segment(aes(xend=down.arrows.x, yend=down.arrows$STOP), 
                 arrow = arrow(length = unit(0.1, "cm")),
                 colour = 'green4') + 
    geom_text_repel(size = 3,
                    aes(label = down.arrows$GENE),
                    color = 'black',
                    segment.color = 'black') +
    theme_classic(base_size = 16)

执行以下操作：

ggplot(down.arrows, aes(down.arrows.x, down.arrows$STOP)) +   # This is all it took
    geom_segment(aes(xend=down.arrows.x, yend=down.arrows$START), # and this
                 arrow = arrow(length = unit(0.1, "cm")),
                 colour = 'green4') + 
    geom_text_repel(size = 3,
                    aes(label = down.arrows$GENE),
                    color = 'black',
                    segment.color = 'black') +
    theme_classic(base_size = 16)