Add summary plot at the end of facet_wrap ggplot

Question

I'd like to add a summary plot at the end of my facet_wrap plot, of what the plot would look like if I hadn't employed the facet_wrap. For example:

test=data.frame(x=runif(1000,min=-1,max=1),y=as.character(sample(x=1:8, size=1000, replace=TRUE)))

ggplot(test, aes(x=x, fill=x)) +
  geom_histogram(show.legend = FALSE)+
  theme_minimal()+
  facet_wrap(~y)

This produces this plot:

However, since I have that extra corner in the lower right, I'd like to add a summary plot of all the data, as if I hadn't employed variable y. It would look like this:

ggplot(test, aes(x=x, fill=x)) +
      geom_histogram(show.legend = FALSE)+
      theme_minimal()+
      ggtitle('All Data')

Is there a way to do this, perhaps with grid.arrange?

Cheers!

Edited to adjust the test data to better represent the real data:

Note, with fake data the following code works, but not with my real data.

bins <- 200
cols <- c("#0072B2",'#253f4b',"#0072B2","#D55E00","#F0E442","#D55E00")
colGradient <- colorRampPalette(cols)
cut.cols <- colGradient(bins)
cuts <- cut

ggplot(test, aes(x=x, fill=cut(x,bins))) +
  geom_histogram(show.legend = FALSE, binwidth = 0.06)+
  geom_histogram(show.legend = FALSE,
    data = ~ transform(.x, y = "All Data")
  ) +
  scale_color_manual(values=cut.cols,labels=levels(cuts)) +
  scale_fill_manual(values=cut.cols,labels=levels(cuts)) +
  scale_x_continuous(breaks=c(-1,0,1), labels=c('dusk', 'dawn','dusk'), limits = c(-1.1,1.1))+
  
  theme_minimal()+
  facet_wrap(~y)

normalizedtime==x, station==y

Answer 1

One option to achieve your desired would be to use a second geom_histogram like so:

library(ggplot2)
set.seed(123)

ggplot(test, aes(x = x)) +
  geom_histogram() +
  geom_histogram(
    data = ~ transform(.x, y = "All Data")
  ) +
  theme_minimal() +
  facet_wrap(~y)

UPDATE Here is the adapted code based on the data you provided via dput. Still puzzled what's the reason for the error you got when you applied the code to your data. Note: I adapted the code to put the "All Data" category last. Additionally, I used a different approach to color the bars using after_stat().

library(ggplot2)

DPHdol$station <- factor(
  DPHdol$station,
  levels = c(unique(DPHdol$station), "All Data")
)

bins <- 100
cols <- c("#0072B2", "#253f4b", "#0072B2", "#D55E00", "#F0E442", "#D55E00")
colGradient <- colorRampPalette(cols)
cut.cols <- colGradient(bins)
cuts <- cut

ggplot(DPHdol, aes(x = normalizedtime)) +
  geom_histogram(
    aes(fill = after_stat(factor(x))),
    bins = bins
  ) +
  geom_histogram(
    aes(fill = after_stat(factor(x))),
    data = ~ transform(.x, station = factor("All Data", levels = levels(station))), 
    bins = bins
  ) +
  scale_color_manual(values = cut.cols, labels = levels(cuts)) +
  scale_fill_manual(values = cut.cols, labels = levels(cuts)) +
  scale_x_continuous(
    breaks = c(-1, 0, 1), 
    labels = c("dusk", "dawn", "dusk"),
    limits = c(-1.1, 1.1)
  ) +
  theme_minimal() +
  facet_wrap(~station) +
  guides(fill = "none")