Is there a way to show overlapping histograms in R without adjusting transparency?

Question

The objective is to show overlapping histograms, but I want to avoid using the alpha adjustment so that the colours remain bright.

Is there a way to do this without adjusting the alpha arg?

Goal is to display the colors shown below:

hist(rnorm(mean=10, n = 1000), col='blue')
hist(rnorm(mean=11, n = 1000), col='red', add=T)

But also show the overlapping area as shown here

hist(rnorm(mean=10, n = 1000), col='blue')
hist(rnorm(mean=11, n = 1000), col=rgb(1,0,0,0.5), add=T)

Similar question that doesn't quite address transparency:

How to create black and white transparent overlapping histograms using ggplot2?

I'd be fine with densities and use of other graphing packages (e.g. lattice, ggplot2, etc).

Edit: I'd like the plots to be filled and the intersecting area to be a different color (e.g. purple where red and blue intersect).

Answer 1

A solution using ggplot2 and geom_density.

library(ggplot2)
library(tidyr)

# create data
set.seed(1234)
df <- data.frame(x = rnorm(1000, 10), y = rnorm(1000, 11)) %>% 
  gather(key, value) # use tidyr::gather to convert from wide to long format

ggplot(df, aes(value, colour = key)) +
  geom_density(show.legend = F) +
  theme_minimal() +
  scale_color_manual(values = c(x = "red", y = "blue"))

# use 'adjust' to adjust density estimation
ggplot(df, aes(value, colour = key)) +
  geom_density(show.legend = F, adjust = .5) +
  theme_minimal() +
  scale_color_manual(values = c(x = "red", y = "blue"))

Histogram

Since alpha is no option, apart from using densities you could stack the histograms on top of each other, although I'd prefer densities, since they are easier to compare.

# using stacked histograms
ggplot(df, aes(value, fill = key)) +
  geom_histogram(show.legend = F) +
  theme_minimal() +
  scale_fill_manual(values = c(x = "red", y = "blue"))
#> `stat_bin()` using `bins = 30`. Pick better value with `binwidth`.