`guides = "collect"` does not work when using different themes

[z3tt]

Hi Thomas,

I just noticed that applying two different themes breaks the guide merging logic.

library(ggplot2)
library(patchwork)

p1 <- ggplot(mpg, aes(hwy, displ, color = drv)) +
    geom_point()

p2 <- ggplot(mpg, aes(cty, displ, color = drv)) +
    geom_point() + 
    theme_minimal()

(p1 + p2) + plot_layout(guides = "collect") &
    theme(legend.position = "bottom")

^{Created on 2026-03-16 with reprex v2.1.1}

Guess that's a decision (or maybe also technical difficulty?) as it'd need to decide which theme to apply to the legend.

Not sure it ever worked before but it would be kinda neat to have an option to combine differently themed plots. Do you think that's possible?

[teunbrand]

Hi Cédric,

Patchwork merges guides that are identical on the grid level. It doesn't know about the ggplot2-level properties of guides (for example it doesn't know if they share breaks or glyphs or anything of the sort).

To merge legends affected by different themes, you need to force them to use the same theme (or otherwise ensure they're styled identically).

In the example below, we're forcing the first plot's legend to adapt to the same theme as the second plot.

library(ggplot2)
library(patchwork)

p1 <- ggplot(mpg, aes(hwy, displ, color = drv)) +
  geom_point() +
  guides(color = guide_legend(theme = theme_minimal()))

p2 <- ggplot(mpg, aes(cty, displ, color = drv)) +
  geom_point() + 
  theme_minimal()

(p1 + p2) + plot_layout(guides = "collect") &
  theme(legend.position = "bottom")

^{Created on 2026-03-16 with reprex v2.1.1}

[z3tt]

Nice example for the guide_legend() functionality! While preparing a "real-life" use case I also realized that one can use the same theme and then modify one plot as well.

Closing this issue, but adding this example for the sake of completeness:

library(ggplot2)
library(patchwork)

g1 <- ggplot(mpg, aes(hwy, displ, color = drv)) +
    geom_point() +
    theme_minimal()

g2 <- ggplot(mpg, aes(drv, displ,  color = drv)) +
    geom_boxplot(color = "grey30") +
    geom_jitter(width = .1) + 
    theme_minimal()

## modify on the fly
((g1 + theme(panel.border = element_rect(color = "grey30", fill = NA))) + g2) + 
    plot_layout(guides = "collect") &
    theme(legend.position = "bottom")

## or change plot directly
g1b <- ggplot(mpg, aes(hwy, displ, color = drv)) +
    geom_point() +
    theme_minimal() +
    theme(panel.border = element_rect(color = "grey30", fill = NA))

(g1b + g2) + 
    plot_layout(guides = "collect") &
    theme(legend.position = "bottom")

^{Created on 2026-03-16 with reprex v2.1.1}