In base R, we can use the function hist() to create the density histogram of a given variable, say x. If we write:

  h <- hist(x, freq=FALSE)

then, h$mids is a vector containing the mid-point value for each bin, and h$density contains the density for each bin. I want to draw my density histogram with ggplot2 with geom_histogram().

Is there any way to retrieve the similar values (mid-point and density of each bin) from the ggplot2 functions?

CodePudding user response：

You can accomplish this by creating a histogram using ggplot() geom_histogram(), and then use ggplot_build() to extract the bin midpoints, min and max values, densities, counts, etc.

Here's a simple example using the built-in iris dataset:

library(ggplot2)

# make a histogram using the iris dataset and ggplot()
h <- ggplot(data = iris)  
  geom_histogram(mapping = aes(x=Petal.Width),
                 bins = 11)

# extract the histogram's underlying features using ggplot_build()
vals <- ggplot_build(h)$data[[1]]

# print the bin midpoints
vals$x
## 0.00 0.24 0.48 0.72 0.96 1.20 1.44 1.68 1.92 2.16 2.40

# print the bin densities
vals$density
## 0.1388889 1.0000000 0.2500000 0.0000000 0.1944444 0.5833333 0.5555556 0.5000000 0.3055556 0.2500000 0.3888889