[R] How to use RColorBrewer in ggplot2?

[Luigi Marongiu]

Thank you, that worked fine.
May I also ask how to create a vector of colors with RColorBrewer?
Let's say I wanted to color z with 4 shade colors from the "Paired"
palette, but then assign the fifth with a color of my choice, say
"black", to distinguish clearly the fifth class.
If I run
```
> scale_fill_brewer(palette="BrBG")
<ggproto object: Class ScaleDiscrete, Scale, gg>
    aesthetics: fill
    axis_order: function
    break_info: function
    break_positions: function
    breaks: waiver
    call: call
    clone: function
    dimension: function
    drop: TRUE
    expand: waiver
    get_breaks: function
    get_breaks_minor: function
    get_labels: function
    get_limits: function
    get_transformation: function
    guide: legend
    is_discrete: function
    is_empty: function
    labels: waiver
    limits: NULL
    make_sec_title: function
    make_title: function
    map: function
    map_df: function
    n.breaks.cache: NULL
    na.translate: TRUE
    na.value: NA
    name: waiver
    palette: function
    palette.cache: NULL
    position: left
    range: environment
    rescale: function
    reset: function
    train: function
    train_df: function
    transform: function
    transform_df: function
    super:  <ggproto object: Class ScaleDiscrete, Scale, gg>
```
while the help says "The brewer scales provide sequential, diverging
and qualitative colour schemes".
How can I generate 4 shades with RColorBrewer?
Thanks.

On Thu, Aug 14, 2025 at 10:00 AM Marttila Mikko
<mikko.marttila using orionpharma.com> wrote:
>
> Hi Luigi,
>
> As you map z to colour, you need scale_colour_brewer, not the fill version.
> And to get discrete colours, you need to make z discrete. A separate group
> mapping isn't needed in this case. Try this:
>
>     ggplot(df, aes(x=x, y=y, colour=factor(z))) +
>       geom_point(size=4) +
>       scale_colour_brewer(palette = "Paired")
>
> Best,
>
> Mikko
>
> -----Original Message-----
> From: R-help <r-help-bounces using r-project.org> On Behalf Of Luigi Marongiu
> Sent: Thursday, 14 August 2025 06:25
> To: r-help <r-help using r-project.org>
> Subject: [R] How to use RColorBrewer in ggplot2?
>
> Hello,
> I would like to define a color range to custom color some plot, specifically made in ggplot2 (but also for normal plots).
> I have been trying to use RColorBrewer but I don't get any value out of this function. I expected it would create a vector of color values, but I must be missing something.
> What is the correct you of this function?
> Thank you.
>
> EXAMPLE
> ```
> set.seed(50)
> df = data.frame(x = runif(15, 0, 1),
>                 y = x^2 + runif(15, 0, 1),
>                 z = rep(1:5, 3))
> library(ggplot2)
> library(RColorBrewer)
> ggplot(df, aes(x=x, y=y, colour=z, group=z)) +
>   geom_point(size=4) +
>   scale_fill_brewer(palette = "Paired")
> ```
>
>
> --
> Best regards,
> Luigi
>
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-- 
Best regards,
Luigi