[R] How to customize legend labels in ggplot2?

[Rui Barradas]

Às 10:35 de 12/03/2025, Luigi Marongiu escreveu:
> I have a data frame with measurements in different conditions. I set
> the conditions as a factor using a notation for ease of use. I now
> want to plot the data and assign meaningful labels to the factors. I
> am using ggplot2; for the x axis I would like to keep the factors but
> in the legend I would like to use custom values.
> I tried different combinations but none worked.
> What is the correct way to assign
> custom labels to legends in ggplot2?
> Thank you
> 
> EXAMPLE:
> ```
> df = data.frame(Target = 1:4,
>                  Rate = c(0.02078663, 0.03685543, 0.02238002, 0.05033979),
>                  SD = c(0.003043398, 0.001447410, 0.002998729, 0.002171813))
> df$Target = factor(df$Target)
> ggplot(df, aes(x=Target, y=Rate, colour=Target, group=Target)) +
>    geom_point(size=8) +
>    geom_errorbar(aes(ymin=Rate-SD, ymax=Rate+SD), width=.1) +
>    scale_colour_manual(values = COLS) +
>    xlab(expression(bold("Class"))) +
>    ylab(expression(bold("Value"))) +
>    theme_classic(base_size = 15)
> ```
> NOTE: if using
> ```
> ...
>    theme_classic(base_size = 15, labels = c("Condition 1", "Condition 2",
>                                             "Condition 3", "Control"))
> ```
> I get the error:
> 
> Error in theme_classic(base_size = 15, labels = c("Condition 1",
> "Condition 2",  :
>    unused argument (labels = c("Condition 1", "Condition 2", "Condition
> 3", "Control"))
> 
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Hello,

The colors COLS are missing from the question.
As for the labels, use


lbls <- c("Condition 1", "Condition 2", "Condition 3", "Control")

and then

scale_colour_manual(values = COLS, labels = lbls)


Hope this helps,

Rui Barradas


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