ggplot2 中的手动图例错误

Question

I'd like to insert the correct legend into the graphic. In other words, a red triangle and a blue circle in legend. Below I showed a MWE.

df1 <- data.frame(x = 1 : 10, y = rnorm(10))
df2 <- data.frame(x = 1 : 10, y = runif(10))

g <- ggplot()
g <- g + geom_point(aes(x = x, y = y, color = 'color1'), data = df1, shape = 19, size = 2)
g <- g + geom_point(aes(x = x, y = y, color = 'color2'), data = df2, shape = 17, size = 3)
g <- g + scale_colour_manual(breaks = c('color1', 'color2'), 
                             values = c('color1' = 'blue', 'color2' = 'red'))
g + theme_bw()

Answer 1

The shapes aren't mapped variables in your example, so the guide doesn't attempt to merge the shape legend (since it doesn't exist) with the colour legend. You could map the shapes as follows, with a manual scale:

library(ggplot2)
df1 <- data.frame(x = 1 : 10, y = rnorm(10))
df2 <- data.frame(x = 1 : 10, y = runif(10))

g <- ggplot()
g <- g + geom_point(aes(x = x, y = y, color = 'color1', shape = "color1"), 
                    data = df1, size = 2)
g <- g + geom_point(aes(x = x, y = y, color = 'color2', shape = "color2"), 
                    data = df2, size = 3)
g <- g + scale_colour_manual(breaks = c('color1', 'color2'), 
                             values = c('color1' = 'blue', 'color2' = 'red'))
# We need to name the shape legend 'colour' so ggplot knows it belongs to the same legend
g + scale_shape_manual(values = c(19, 17), name = "colour")

^{Created on 2020-04-18 by the reprex package (v0.3.0)}

Alternatively, you can edit the legend itself in the colour scale:

library(ggplot2)
df1 <- data.frame(x = 1 : 10, y = rnorm(10))
df2 <- data.frame(x = 1 : 10, y = runif(10))

g <- ggplot()
g <- g + geom_point(aes(x = x, y = y, color = 'color1'), 
                    data = df1, shape = 19, size = 2)
g <- g + geom_point(aes(x = x, y = y, color = 'color2'), 
                    data = df2, shape = 17, size = 3)
g + scale_colour_manual(breaks = c('color1', 'color2'), 
                        values = c('color1' = 'blue', 'color2' = 'red'),
                        guide = guide_legend(override.aes = list(shape = c(19, 17))))

^{Created on 2020-04-18 by the reprex package (v0.3.0)}