r - 用纯色绘制一条线，用渐变绘制第二条线

Question

我想在一张图表上画两条线，一条是渐变色的，另一条是纯色的。我可以添加单独的线条和渐变:

x <- seq(1, 100, 1)
y <- rnorm(100, 50, 15)
z <- rnorm(100, 30, 5)
df <- data.frame(x,y,z)

library(ggplot2)   
ggplot(df, aes(x = x, y = y, color = x)) + geom_line() +
  scale_color_gradient(low = "blue", high = "red") +
  geom_line(data = df, aes(x = x, y = z, color = x))

但是改变颜色会引发错误:

> ggplot(df, aes(x = x, y = y, color = ..y..)) + geom_line() +
+   scale_color_gradient(low = "blue", high = "red") +
+   geom_line(aes(x = x, y = z, color = "yellow"))
Error: Discrete value supplied to continuous scale

我希望添加标签，但这可能太复杂了......

Answer 1

最简单的方法是在aes 之外为实线指定颜色:

library(ggplot2)
ggplot(df, aes(x, y, color = x)) + 
    geom_line() +
    # No need to respecify data or x at it's defined in main ggplot call
    geom_line(aes(y = z), color = "yellow") +
    scale_color_gradient(low = "blue", high = "red")