change legend title

[adan11]

Hi,
I am combining multiple plots using "cowplot". I want to build one legend. Here is a sample code:

plot_t = function(df,colors){
    p = ggplot(df,aes(s,tr,col=strategy),size=1)+
      geom_line(size=1)+
      scale_x_continuous(breaks = scales::pretty_breaks(n = 5)) +
      scale_y_continuous(breaks = scales::pretty_breaks(n = 10)) +
      labs(x='x',y='y')+
      theme(legend.position = "none",
            legend.title = element_text(size=18),
            legend.text = element_text(size=18),
            axis.title = element_text(size=18),
            axis.text = element_text(size=16,color="black"),
            #axis.text.x = element_text(angle = 90),
            panel.grid.major.x = element_blank(),
            panel.grid.minor.x = element_blank(),
            panel.grid.major.y = element_line(colour = "gray50", linetype="dashed"),
            
            panel.background = element_blank(), 
            axis.line = element_line(colour = "black")
      )+
      scale_fill_manual(values = colors)+
      scale_color_manual(values = colors)
    return(p)
  }
 rplots <- plot_grid(
    plot_t,ploy_i,ploy_c,
    align = 'vh',
    labels = "AUTO",
    hjust = -1,
    nrow = 1
  )
 
  legend_b = get_legend(
    plot_t + 
      guides(color = guide_legend(nrow = 1))+
      theme(legend.position = "bottom"))
 plots = plot_grid(rplots, legend_b, ncol = 1, rel_heights = c(1, .1))

It worked, but I just want to set the legend title manually. I tried to add the title in labs. Two legends were created. I would appreciate any suggestion.

Thanks

[JackDavison]

It may be useful if you provide what "t", "i" and "c" look like. Though have you thought about using patchwork over cowplot? It's a more modern, simple way of achieving plot alignment:

The Composer of Plots

library(tidyverse)
library(patchwork)

plt = ggplot(mtcars, aes(mpg, disp, color = cyl)) +
  geom_point()

# default patchwork

plt + plt + plt

# tag & collect legends, put legend at bottom

plt + plt + plt +
  plot_annotation(tag_levels = "A") +
  plot_layout(nrow = 1, guides = "collect") &
  theme(legend.position = "bottom")

^{Created on 2022-02-11 by the reprex package (v2.0.1)}

[adan11]

Thanks, I checked Patchwork, still can not figure out, how to set the title for the legend manually.