如何在GGPLOT2传奇中向后和向前的方向显示箭头？

Question

我有一个 dataFrame ，上面有箭头的坐标：

arrows = data.frame(direction = factor(c("forward", "backward", "backward")),
                x = c(0, 0, 0),
                xend = c(1, 1, 1),
                y = c(1, 1.2, 1.1),
                yend = c(1, 1.2, 1.1))

我想使用此数据绘制箭头 - 有些朝向前进方向，反之亦然。

到目前为止，我尝试了

library(ggplot2)

ggplot() +
        geom_segment(data = arrows, 
                     aes(x, y, xend = xend, yend = yend, col = direction),
                     arrow = arrow(length = unit(0.3, "cm"), type = "closed", ends = c("last", "first")))

：

我想在此图中解决两个问题：

1. 我如何确保 ggplot '理解' “前进”和“向后”，所以它给了他们正确的传奇吗？

2. 如何更改图例，以便它以向前向前的箭头和向后的向后箭头显示向前的方向？

Answer 1

也许有两个传说，一个使用自定义字形？

draw_key_arrow_left <- function(data, params, size, dir) {
  if (is.null(data$linetype)) {
    data$linetype <- 0
  } else {
    data$linetype[is.na(data$linetype)] <- 0
  }
  
  segmentsGrob(0.9, 0.5, 0.1, 0.5,
               gp = gpar(
                 col = alpha(data$colour %||% data$fill %||% "black", data$alpha),
                 # the following line was added relative to the ggplot2 code
                 fill = alpha(data$colour %||% data$fill %||% "black", data$alpha),
                 lwd = (data$size %||% 0.5) * .pt,
                 lty = data$linetype %||% 1,
                 lineend = "butt"
               ),
               arrow = params$arrow
  )
}


arrows2 <- arrows %>%
  mutate(x_orig = x, xend_orig = xend,
         x = if_else(direction == "forward", x_orig, xend_orig),
         xend = if_else(direction == "forward", xend_orig, x_orig))

ggplot() +
  geom_segment(data = arrows2 %>% filter(direction == "forward"),
               aes(x, y, xend = xend, yend = yend, col = direction),
               arrow = arrow(length = unit(0.3, "cm"), type = "closed")) +
  scale_color_manual(values = "#F8766D") +
  
  ggnewscale::new_scale_color() +
  geom_segment(data = arrows2 %>% filter(direction == "backward"),
               aes(x, y, xend = xend, yend = yend, col = direction),
               arrow = arrow(length = unit(0.3, "cm"), type = "closed"),
               key_glyph = "arrow_left") +
  scale_color_manual(values = "#619CFF", name = "") +
  theme(legend.key.width=unit(0.7,"cm"))

Answer 2

如何将“方向”映射到“第一个”和“最后”，例如，

ggplot() +
  geom_segment(data = arrows, 
                 aes(x = x, xend = xend, y = y, yend = yend, col = direction),
               arrow = arrow(length = unit(0.3, "cm"), type = "closed", ends = ifelse(arrows$direction == "forward", "first", "last" ))) +
  scale_colour_manual(values = c("darkred", "darkblue"), labels = c("forward", "backward"))

我还使用 scale_colour_manual 来控制哪个方向是向前且向后的。

关于传说中的自定义字形的另一个问题 - - 这应该允许不同的箭头方向，但可能不值得。

Answer 3

需要为每个箭头设置端的参数，而您的末端仅是两个长度，因此最后一个箭头将是错误的方向，因为它使用的是“最后”的默认值，但是由于箭头向后移动，它应该是“第一个”

arrows <- data.frame(direction = (c("forward", "backward", "backward")),
                    x = c(0, 0, 0),
                    xend = c(1, 1, 1),
                    y = c(1, 1.2, 1.1),
                    yend = c(1, 1.2, 1.1))

arrow_head <- function(direction) {
  if(direction == "backward") {
    return("first")
  } else {
    return("last")
  }
}

ggplot() +
  geom_segment(data = arrows,
               aes(x, y, xend = xend, yend = yend, col = direction),
               arrow = arrow(length = unit(0.3, "cm"), type = "closed", ends = lapply(arrows$direction, arrow_head)))

Answer 4

您可以根据方向列以X/XEND交换列值。

library(tidyverse)
arrows = data.frame(direction = factor(c("forward", "backward", "backward")),
                    x = c(0, 0, 0),
                    xend = c(1, 1, 1),
                    y = c(1, 1.2, 1.1),
                    yend = c(1, 1.2, 1.1))

## thanks for the idea https://stackoverflow.com/questions/51096664/how-to-do-conditional-swapping-using-two-columns
swap_direction <- function(data){
  swap <- data$direction == "backward"
  v1 <- data$x
  v2 <- data$xend
  data$x[swap] <- v2[swap]
  data$xend[swap] <- v1[swap]
  data
}
reversed_arrows <- swap_direction(arrows)

ggplot() +
  geom_segment(data = reversed_arrows, 
               aes(x, y, xend = xend, yend = yend, col = direction),
               arrow = arrow(length = unit(0.3, "cm"), type = "closed"))

^{在2022-06-28上创建的 reprex软件包（v2.0.1）}