Data

Firstly, we create an example data with different distributions.

# Create example data 
data <- data.frame(
  type = c( rep("variable 1", 1000), rep("variable 2", 1000) ),
  value = c( rnorm(1000), rnorm(1000, mean=4) )
)

Several histograms on the same axis

If the number of group or variable you have is relatively low, you can display all of them on the same axis, using a bit of transparency to make sure you do not hide any data.

library(ggplot2)
library(dplyr)
library(hrbrthemes) # library for themes

#multi histogram
multi <- data %>%
  ggplot( aes(x=value, fill=type)) +
    geom_histogram( color="#e9ecef", alpha=0.6, position = 'identity') +
    scale_fill_manual(values=c("#69b3a2", "#404080")) +
    theme_ipsum() +
    labs(fill="")

multi

Histogram with several groups

Data

Several histograms on the same axis

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