ggplot2 guide_color_bar cannot put label at beginning and end of the legend elements

Question

I am trying to plot some data ranges from 1 to 6 using scale_color_gradientn (ggplot2 package) based on the following code. By default, guide_color_bar will put the label as the "center" of the bin in legend (see code block 1). But I would like to set the label to be at the "upper" and "lower" boundary of each bin. I tried to set breaks and labels accordingly, however, the 2,3,4,5 is properly aligned but 1,6 is not showing (see code block2).

Please see code attached.

library(ggplot2)

###provide dataset 
dat    <- data.frame(list(x = c(0.214137620411313,0.553775825041679,-1.0595195186151,
                                -1.61004932625145,-0.338151062634607,0.204937753426245,
                                -0.224345039271189,-0.909609704018834,-0.808109884248038,
                                0.553083514142192,-0.389177932603183,-0.447245638594407,
                                -0.0211388451690059,-0.599417455124725,-0.310866189554078,
                                -0.681632468885545,-0.202055723512808,1.11680032924059,0.82599921267075,1.2509189798129),
                          y = c(2.60809809498069,-0.051039961195504,2.22719419433773,-0.0138721238155097,-1.54739969676097,
                                -1.37988910915699,1.47987074083825,-0.254921944338877,-0.326280380145921,-0.726638665692272,
                                -1.95234864995199,0.422940041768889,1.18168478575317,0.91795937727616,0.0954675468852296,
                                -1.68443178674375,0.990329350606127,-0.707831781928625,-0.594029169314093,-1.06589703339072)),
                     z = c(1,3,3,1,2,2,2,4,2,1,1,1,1,5,2,4,3,4,1,4))
###define breaks and colors

my_breaks <- c(0,1,2,3,4,5,6)
colors <- c('#e41a1c','#377eb8','#4daf4a',
            '#ff7f00','#ffff33','#a65628')
###the label is in the center.
ggplot(dat, aes(x,y,color=z, label = round(z,2))) + geom_point() +
  scale_color_gradientn(
    colours = colors,
    values  = scales::rescale(c(1:6)),
    limit   = c(1,6),

    guide = guide_colourbar(nbin = 6, raster = FALSE, frame.colour = "black", ticks.colour = NA,
                            direction = "horizontal", 
                            barwidth = 30, barheight = 2, label.hjust = 0)) + 
  geom_text() +
  theme(legend.position = 'bottom')

###the label shows the upper and lower boundary for each bin, but the beginning (1) and ending (6) is not showing. 


ggplot(dat, aes(x,y,color=z, label = round(z,2))) + geom_point() +
  scale_color_gradientn(
    colours = colors,
    values  = scales::rescale(c(1:6)),
    limit   = c(1,6),
    breaks  = c(1:7)-0.5, ###the label should be at 0.5,1.5,2.5,...,6.5
    labels  = my_breaks,
    guide = guide_colourbar(nbin = 6, raster = FALSE, frame.colour = "black", ticks.colour = NA,
                            direction = "horizontal", 
                            barwidth = 30, barheight = 2, label.hjust = 0)) + 
  geom_text() +
  theme(legend.position = 'bottom')

Any help is appreciated.

Related (I think): [Create discrete color bar with varying interval widths and no spacing between legend levels](https://stackoverflow.com/questions/50506832/create-discrete-color-bar-with-varying-interval-widths-and-no-spacing-between-le), and corresponding issue with some alternatives: [Provide a guide that has discrete colors, but labels shifted between them to highlight intervals](https://github.com/tidyverse/ggplot2/issues/2673), e.g. [this](https://github.com/tidyverse/ggplot2/issues/2673#issuecomment-402878574) — Henrik, Jun 14 '19 at 07:47
Thank you very much for providing the two links. I am working on the first link. The second reference did not work. ggplot(dat, aes(x,y,color=z)) + geom_point() + scale_colour_discrete_gradient( colours = colors, limits = c(1,6), breaks = c(1:7) - 0.5, labels = my_breaks, bins = 6, guide = guide_colourbar(nbin = 6, raster = FALSE, frame.colour = "black", ticks.colour = NA) ) — Tong Qiu, Jun 14 '19 at 12:14

score 0 · Answer 1 · answered Jun 14 '19 at 05:37

Might not be the most elegant, but take a look at the following. I also added some adjustment to your point labels.

library(ggplot2)
#> Registered S3 methods overwritten by 'ggplot2':
#>   method         from 
#>   [.quosures     rlang
#>   c.quosures     rlang
#>   print.quosures rlang

###provide dataset 
dat    <- data.frame(list(x = c(0.214137620411313,0.553775825041679,-1.0595195186151,
                                -1.61004932625145,-0.338151062634607,0.204937753426245,
                                -0.224345039271189,-0.909609704018834,-0.808109884248038,
                                0.553083514142192,-0.389177932603183,-0.447245638594407,
                                -0.0211388451690059,-0.599417455124725,-0.310866189554078,
                                -0.681632468885545,-0.202055723512808,1.11680032924059,0.82599921267075,1.2509189798129),
                          y = c(2.60809809498069,-0.051039961195504,2.22719419433773,-0.0138721238155097,-1.54739969676097,
                                -1.37988910915699,1.47987074083825,-0.254921944338877,-0.326280380145921,-0.726638665692272,
                                -1.95234864995199,0.422940041768889,1.18168478575317,0.91795937727616,0.0954675468852296,
                                -1.68443178674375,0.990329350606127,-0.707831781928625,-0.594029169314093,-1.06589703339072)),
                     z = c(1,3,3,1,2,2,2,4,2,1,1,1,1,5,2,4,3,4,1,4))
###define breaks and colors

my_breaks <- c(0,1,2,3,4,5,6)
colors <- c('#e41a1c','#377eb8','#4daf4a',
            '#ff7f00','#ffff33','#a65628')

# Charting
ggplot(dat, aes(x,y,color=z, label = round(z,2))) + geom_point() +
  scale_color_gradientn(
    colours = colors,
    values  = scales::rescale(c(1:6)),
    limit   = c(1,6), # Changed the limit to 1:6
    breaks  = c(1:6), # Set the breaks to 1:6
    labels  = c(1,2,3,4,5,6), # Set the labels manually
    guide = guide_colourbar(nbin = 6, raster = FALSE, frame.colour = "black", ticks.colour = NA,
                            direction = "horizontal", 
                            barwidth = 30, barheight = 2, label.hjust = -6.5)) + # Set the adjustment to -6.5
  geom_text(hjust = -1, vjust = -0.3) +
  theme(legend.position = 'bottom')

^{Created on 2019-06-14 by the reprex package (v0.3.0)}

You might want to visualise this in another way. The point labelling is not really needed, since you are already using colors in reference to the scale. — larsoevlisen, Jun 14 '19 at 05:42
Yes. I agree with you, the text is just checking if the color is correctly labeled. In addition, is it possible to add a “0” at the lower end as well? — Tong Qiu, Jun 14 '19 at 11:25

ggplot2 guide_color_bar cannot put label at beginning and end of the legend elements

1 Answers1