R ggpubr：将图例标题移至图例键上方

Question

I am struggling with the legend position within ggpubr. I know that I can modify the legend position pe by ggpar(legend = "bottom") . But, how to place legend title above the legend keys?

In ggplot2 , it seems that guide_legend(title.position = "top") should do this, but how to make it work with ggpubr ? (thanks to @c06n and link here: https://ggplot2.tidyverse.org/reference/guide_legend.html ). I would like to combine the ggplot2 and ggpubr but I don't know exactly why.

Dummy example:

df2 <- data.frame(supp=rep(c("VC", "OJ"), each=3),
                  dose=rep(c("D0.5", "D1", "D2"),2),
                  len=c(6.8, 15, 33, 4.2, 10, 29.5))

# Plot "len" by "dose" and
# Change line types and point shapes by a second groups: "supp"
p<- ggline(df2, "dose", "len",
       linetype = "supp", shape = "supp",
       color = "supp", palette = c("#00AFBB", "#E7B800"))

# Seems not working
ggpar(p,
  linetype = guide_legend(title = "My title", title.position = "top"))

Answer 1

I do not know ggpubr , it seems like a wrapper for ggplot2 . If that is true, and/or it has implemented the same functionality as ggplot2 , you should be able to achieve that via legend guide , see here . I think it is title.position you need to adjust.

If you cannot achieve that with ggpubr , I suggest using ggplot2 instead, perhaps adjusting the theme to your needs.

Edit. @markus has the answer, so to put it all in one place:

p <- ggline(df2, "dose", "len",
           linetype = "supp", 
           shape = "supp",
           color = "supp", 
           palette = c("#00AFBB", "#E7B800")) +
  guides(color = guide_legend(title.position = "top", 
                              title.hjust = 0.5))

Interesting question though from @Bruno Pinheiro as to why only color (and fill ) will work, but not shape or linetype . This would be relevant if the plot needs to be monochrome. All three should work equally well as grouping factors.

Does anyone have an idea?

Answer 2

These options are working here.

With ggpubr :

df2 <- data.frame(supp=rep(c("VC", "OJ"), each=3),
                  dose=rep(c("D0.5", "D1", "D2"),2),
                  len=c(6.8, 15, 33, 4.2, 10, 29.5))

library(ggpubr)
p <- ggline(df2, "dose", "len",
       linetype = "supp", shape = "supp",
       color = "supp", palette = c("#00AFBB", "#E7B800"))

p + guides(colour = guide_legend(title.position = "top"))

I don't know why, but if i set the guide for another aesthetic the legend title position do not change:

p + guides(shape = guide_legend(title.position = "top"))
p + guides(linetype = guide_legend(title.position = "top"))

It's a good question to be made for ggplot2 experts.

And here is the same working in ggplot2 :

library(ggplot2)
ggplot(df2, aes(x = dose, y = len, colour = supp)) +
  geom_line(aes(group = supp, linetype = supp)) +
  geom_point(aes(shape = supp)) +
  scale_colour_manual(values = c("#00AFBB", "#E7B800")) +
  theme_classic() +
  theme(legend.position = "top") +
  guides(colour = guide_legend(title.position = "top"))