R 在GG图中绘制射线的自动程序

发布于03月05日

在R和ggplot2中，绘制lines和segment很容易，但绘制射线更难.我想知道是否存在在两个点之间绘制射线的解决方案；一个定义为原点(下面代码显示的图形中的红点)，光线通过第二个点(下面代码显示的图形中的黑点).以下是我为此编写的一段代码:

require(dplyr)
require(ggplot)

set.seed(123)
n <- 4

dat <-
  data.frame(
  X = rnorm(n),
  Y = rnorm(n))

centroid <- 
  dat %>%
  dplyr::summarise(across(c(X,Y), mean))

ggplot(data = dat, aes(X,Y)) +
  geom_point() +
  geom_point(data = centroid, aes(X, Y), col = "red") +
  geom_segment(x = centroid$X, y = centroid$Y,
               xend = dat$X, yend = dat$Y)

go 年也开设了一个类似的话题:ggplot - how to draw rays?个，但它并不完全符合我的担忧，因为我想避免三角学，我想让这个问题自动化.

我们非常欢迎任何帮助、建议或替代解决方案.

推荐答案

你可以编写你自己的geom，就像他们在另一个问题中所做的那样.这是另一个可能的解决方案

geom_ray <- function(mapping = NULL, data = NULL,
                        ...,
                     na.rm = FALSE,
                     show.legend = NA) {
  
  layer(
    data = data,
    mapping = mapping,
    stat = StatIdentity,
    geom = GeomRay,
    position = PositionIdentity,
    show.legend = show.legend,
    inherit.aes = FALSE,
    params = rlang::list2(
      na.rm = na.rm,
      ...
    )
  )
}

GeomRay <- ggproto("GeomRay", Geom,
    draw_panel = function(data, panel_params, coord, lineend = "butt") {
      ranges <- coord$backtransform_range(panel_params)
      
      if (coord$clip == "on" && coord$is_linear()) {
        # Ensure the line extends well outside the panel to avoid visible line
        # ending for thick lines
        ranges$x <- ranges$x + c(-1, 1) * diff(ranges$x)
      }

      slope <- (data$towardy - data$y)/(data$towardx - data$x)
      intercept <- data$y - data$x*slope
      data$x    <- data$x
      data$y    <- data$y
      data$xend    <- ifelse(data$towardx > data$x, 
                             ranges$x[2],
                             ranges$x[1]
      )
      data$yend <- ifelse(data$towardx > data$x, 
                          ranges$x[2] * slope + intercept,
                          ranges$x[1] * slope + intercept
                          )
      
      GeomSegment$draw_panel(ggplot2:::unique0(data), panel_params, coord, lineend = lineend)
    },
    
    default_aes = aes(colour = "black", linewidth = 0.5, linetype = 1, alpha = NA),
    required_aes = c("x", "y", "towardx", "towardy"),
    
    draw_key = draw_key_abline,
    
    rename_size = TRUE,
    
    check_constant_aes = FALSE
)

这个代码基本上直接从ggplot::geom_abline代码改编而来.

在此设置中，x和y是希望光线开始的位置，然后towardx和towardy是希望光线指向的方向.因此，对于您的数据，您可以这样使用它

ggplot(data = dat, aes(X,Y)) +
  geom_point() +
  geom_point(data = centroid, aes(X, Y), col = "red") +
  geom_ray(x = centroid$X, y = centroid$Y,
               aes(towardx = X, towardy = Y))

which produces