modify scale in existing ggplot object without replacing the scale

Question

I have a ggplot object. It has an x-axis label that was created by scales_x_continuous(). Without recreating the plot, and without changing any of the other arguments that were passed to scale_x_continuous(), I want to change the x-axis label. How may I do this?

There are many SO posts about updating ggplot objects after they have been created. But as best I can tell, the solutions in those posts don't apply to this particular situation. To fix ideas, here is a small example:

library(ggplot2)
p <- ggplot(mtcars, aes(mpg, wt)) + 
  geom_point() + 
  scale_x_continuous(name = "oldLabel", limits = c(15, 30))

I want to change the x-axis label from "oldLabel" to "newLabel" without overriding the limits argument. Many seemingly obvious strategies mentioned in other posts don't work in this case:

1. p + scale_x_continuous(name = "newLabel") changes the label -- but it also changes the limits. I could get around that problem by calling p + scale_x_continuous(name = "newLabel, limits = c(15, 30)"). But in practice, the ggplot objects that I use may be created with many arguments to scale_x_continuous(), and I don't want to repeat them all just to override the x-axis label.

2. p + xlab("newLabel") doesn't replace the label. That is, xlab() seems to have no effect in this case. It would work if the original label had been specified with xlab(), but that isn't the case here.

3. update_labels(p, list(x = "new x label")) also doesn't replace the label.

4. ggplot_build() also seems to have no effect, at least as I've been using it:

library(gridExtra)
tmp <- ggplot_build(p)
tmp$layout$panel_params[[1]]$x$name     <- "newLabel"
tmp$layout$panel_params[[1]]$x.sec$name <- "newLabel"
grid.arrange(ggplot_gtable(tmp))

Answer 1

You need to update the name parameter of the x scale object within the plot itself (not the copy that resides in the layout of a ggplot built object).

Here's a full reprex:

library(ggplot2)

p <- ggplot(mtcars, aes(mpg, wt)) + 
  geom_point() + 
  scale_x_continuous(name = "oldLabel", limits = c(15, 30))

p
#> Warning: Removed 9 rows containing missing values (geom_point).

p$scales$scales[[1]]$name <- "newLabel"

p
#> Warning: Removed 9 rows containing missing values (geom_point).

^{Created on 2020-09-01 by the reprex package (v0.3.0)}