Reverse the legend order when using ggplotly()

Question

I would like to reverse the order of the legend for a horizontal bar chart. When adding guides(fill = guide_legend(reverse = TRUE)) to the ggplot it works fine (see second plot). However, after applying ggplotly() the legend is again in the default order.

How to reverse the order of the plotly legend without changing the order of the bars?

library(ggplot2)
library(dplyr)
data(mtcars)

p1 <- mtcars %>%
  count(cyl, am) %>%
  mutate(cyl = factor(cyl), am = factor(am)) %>%
  ggplot(aes(cyl, n, fill = am)) +
  geom_col(position = "dodge") +
  coord_flip()
p1

p2 <- p1 + guides(fill = guide_legend(reverse = TRUE))
p2

plotly::ggplotly(p2)

Answer 1

Adding to the great answer of @Zac Garland here is a solution that works with legends of arbitrary length:

library(ggplot2)
library(dplyr)

reverse_legend_labels <- function(plotly_plot) {
  n_labels <- length(plotly_plot$x$data)
  plotly_plot$x$data[1:n_labels] <- plotly_plot$x$data[n_labels:1]
  plotly_plot
}

p1 <- mtcars %>%
  count(cyl, am) %>%
  mutate(cyl = factor(cyl), am = factor(am)) %>%
  ggplot(aes(cyl, n, fill = am)) +
  geom_col(position = "dodge") +
  coord_flip()

p2 <- mtcars %>%
  count(am, cyl) %>%
  mutate(cyl = factor(cyl), am = factor(am)) %>%
  ggplot(aes(am, n, fill = cyl)) +
  geom_col(position = "dodge") +
  coord_flip()

p1 %>%
  plotly::ggplotly() %>%
  reverse_legend_labels()

p2 %>%
  plotly::ggplotly() %>%
  reverse_legend_labels()