区别主题图例位置和show.legend

Question

I am studying ggplot2 Elegant Graphics for Data Analysis. What difference both code are?

ggplot(mpg, aes(displ, hwy, colour = class)) +
  geom_point(show.legend = FALSE) + 
  directlabels::geom_dl(aes(label = class), method = "smart.grid")


ggplot(mpg, aes(displ, hwy, colour = class)) +
  geom_point() + 
  theme(legend.position = "none") +
  directlabels::geom_dl(aes(label = class), method = "smart.grid")

both create this plot

I wonder when I use show.legend = FALSE

Answer 1

From ?geom_point

show.legend: logical. Should this layer be included in the legends? 'NA', the default, includes if any aesthetics are mapped. 'FALSE' never includes, and 'TRUE' always includes. It can also be a named logical vector to finely select the aesthetics to display.

From ?theme

legend.position: the position of legends ("none", "left", "right", "bottom", "top", or two-element numeric vector)

theme(legend.position = "none") disables all legends, geom_point(..., show.legends = FALSE) disables the legend for this (ie the geom_point ) layer.

---

For example

ggplot(mpg, aes(displ, hwy, colour = class)) +
  geom_point(show.legend = FALSE) +
  geom_label(aes(label = class)) + 
  directlabels::geom_dl(aes(label = class), method = "smart.grid")

shows no legend for geom_point , but does show a legend for geom_label .

---

On the other hand,

ggplot(mpg, aes(displ, hwy, colour = class)) +
  geom_point() +
  geom_label(aes(label = class)) + 
  theme(legend.position = "none") +
  directlabels::geom_dl(aes(label = class), method = "smart.grid")

disables all legends.