[R] How to customize legend labels in ggplot2?

[Thierry Onkelinx]

Dear Luigi,

ggplot2 will use the factor levels as default values for the legend labels.
Setting the factor labels of your target values fixes your problem.

Best regards,



ir. Thierry Onkelinx
Statisticus / Statistician

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FOREST
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Op wo 12 mrt 2025 om 11:36 schreef Luigi Marongiu <marongiu.luigi using gmail.com
>:

> 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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