R facet_wrap and geom_density with multiple groups-CodePudding

Here's my dataframe:

df <- data.frame(state = sample(c(0, 1), replace = TRUE, size = 100),
                 X1 = rnorm(100, 0, 1),
                 X2 = rnorm(100, 1, 2),
                 X3 = rnorm(100, 2, 3))

What I would like to do is to plot for each variable X1, X2, X3 two densities/histograms (given the value of state) on the same plot BUT in such a way that all of the plots are on the same facet. I've done these things separately:

ggplot()   
  geom_density(data = df, aes(x = X1, group = state, fill = state), alpha = 0.5, adjust = 2)   
  xlab("X1")  
  ylab("Density")

ggplot(gather(df[df$state == 0, 2:4]), aes(value))   
  geom_density()   
  facet_wrap(~key, scales = 'free_x')

but I struggle to make it work together.

CodePudding user response：

I'm assuming that you want the three facets for variables X1, X2 and X3, each with two curves filled by state.

You'll need to convert state to a factor, to make it a categorical variable, using dplyr::mutate(). I would also use the newer tidyr::pivot_longer() instead of gather: this will generate columns name value by default.

Your data but with a seed to make it reproducible and named df1:

set.seed(1001)
df <- data.frame(state = sample(c(0, 1), replace = TRUE, size = 100),
                 X1 = rnorm(100, 0, 1),
                 X2 = rnorm(100, 1, 2),
                 X3 = rnorm(100, 2, 3))

The plot:

library(dplyr)
library(tidyr)
library(ggplot2)

df1 %>% 
  pivot_longer(-state) %>% 
  mutate(state = as.factor(state)) %>% 
  ggplot(aes(value))   
  geom_density(aes(fill = state), alpha  = 0.5)   
  facet_wrap(~name)

Result: