Histogram with two variables in ggplot

Question

I have a dataframe with two variables:

DF <- data.frame(Now = as.numeric(c(1, 6, 4, 4, 5, 6)), Before = as.numeric(c(1, 6, 3, 5, 10, 10)))

I can easily plot both variables separately:

library(ggplot2)
ggplot(DF, aes(Now))+
  geom_histogram()
ggplot(DF, aes(Before))+
  geom_histogram()

But I would like to plot both variables together, so that the change between Before and Now is easy to see. One way to do this is described in an answer here: Plot two variables in the same histogram with ggplot. But I would much rather have one plot with differently colored bars side-by-side. How can this be done? (Side note: if it's easier to do with geom_bar than geom_histogram, that works for me too.)

Solution

You need to convert DF to long format using something like tidyr::gather...

library(tidyr)
library(ggplot2)

DF %>% 
  gather(key=Type, value=Value) %>% 
  ggplot(aes(x=Value,fill=Type)) + 
  geom_histogram(position="dodge")

Comments

[Punintended]

Andrew Gustar has already answered this, but it's a duplicate of this question

[KaC]

Thanks. Search didn't return that question.

[Punintended]

Only reason I found it easily is 'cause I checked my answer history ;)