在 ggplot 中制作圆形线端 - 在情节和图例中

Question

我正在尝试将一些图表相互匹配。有些是在 Sigmaplot 中制作的，我无权访问数据。所以这意味着我的新图表必须看起来尽可能相似，我正在使用它ggplot来实现这一点。我添加了 100 万个小细节，使它们更相似，但我仍然无法理解其中一个细节。

线端应该是四舍五入的，我已经通过lineend = "round"在geom_line(). 然而，图例中的线端仍然有一个对接端。我是一个坚持一致性的人，每一个细节都是如此，这意味着我真的不能接受......

这是一个例子。

var1 <- seq(1,100,10)
var2 <- c(1:10)
trt <- c("t1", "t1", "t1", "t1", "t1", "t2", "t2", "t2", "t2", "t2")
my.df <- data.frame(var1, var2, trt)


ggplot(data = my.df, aes(x = var1, y = var2, col = trt))+
  geom_line(size = 3, lineend = "round")

Answer 1

在 ggplot2 包中，图例键geom_line被硬编码为lineend = "butt"：

> GeomLine$draw_key
<ggproto method>
  <Wrapper function>
    function (...) 
f(...)

  <Inner function (f)>
    function (data, params, size) 
{
    data$linetype[is.na(data$linetype)] <- 0
    segmentsGrob(0.1, 0.5, 0.9, 0.5, gp = gpar(col = alpha(data$colour, 
        data$alpha), lwd = data$size * .pt, lty = data$linetype, 
        lineend = "butt"), arrow = params$arrow)
}

我们可以geom_line2()使用图例键定义我们自己的略有不同的版本lineend = "round"：

library(grid)

GeomLine2 <- ggproto(
  "GeomLine2", GeomLine,
  draw_key =  function (data, params, size) {
    data$linetype[is.na(data$linetype)] <- 0
    segmentsGrob(0.3, 0.5, 0.7, 0.5, # I modified the x0 / x1 values here too, to shift
                                     # the start / end points closer to the centre in order
                                     # to leave more space for the rounded ends
                 gp = gpar(col = alpha(data$colour, data$alpha), 
                           lwd = data$size * .pt, 
                           lty = data$linetype, 
                           lineend = "round"),
                 arrow = params$arrow)
  })

geom_line2 <- function (mapping = NULL, data = NULL, stat = "identity", position = "identity", 
                        na.rm = FALSE, show.legend = NA, inherit.aes = TRUE, ...) {
  layer(data = data, mapping = mapping, stat = stat, 
        geom = GeomLine2, # this is the only change from geom_line to geom_line2
        position = position, show.legend = show.legend, inherit.aes = inherit.aes, 
        params = list(na.rm = na.rm, ...))}

结果：

cowplot::plot_grid(

  ggplot(data = my.df, aes(x = var1, y = var2, col = trt))+
    geom_line(size = 3, lineend = "round") +
    ggtitle("original geom_line"),

  ggplot(data = my.df, aes(x = var1, y = var2, col = trt))+
    geom_line2(size = 3, lineend = "round") +
    ggtitle("modified geom_line2"),

  ncol = 1
)