Histogram and Density Plots - R Base Graphs

Pleleminary tasks
Create some data
Create histogram plots: hist()
Create density plots: density()
Related articles
See also
Infos

Previously, we described the essentials of R programming and provided quick start guides for importing data into R.

Here, we’ll describe how to create histogram and density plots in R.

Pleleminary tasks

Launch RStudio as described here: Running RStudio and setting up your working directory
Prepare your data as described here: Best practices for preparing your data and save it in an external .txt tab or .csv files
Import your data into R as described here: Fast reading of data from txt|csv files into R: readr package.

Create some data

The data set contains the value of weight by sex for 200 individuals.

set.seed(1234)
x <- c(rnorm(200, mean=55, sd=5),
     rnorm(200, mean=65, sd=5))
head(x)

## [1] 48.96467 56.38715 60.42221 43.27151 57.14562 57.53028

Create histogram plots: hist()

A histogram can be created using the function hist(), which simplified format is as follow:

hist(x, breaks = "Sturges")

x: a numeric vector
breaks: breakpoints between histogram cells.

Create histograms

hist(x, col = "steelblue", frame = FALSE)

# Change the number of breaks
hist(x, col = "steelblue", frame = FALSE,
     breaks = 30)

Create density plots: density()

The function density() is used to estimate kernel density.

# Compute the density data
dens <- density(mtcars$mpg)
# plot density
plot(dens, frame = FALSE, col = "steelblue", 
     main = "Density plot of mpg")

# Fill the density plot using polygon()
plot(dens, frame = FALSE, col = "steelblue", 
     main = "Density plot of mpg") 
polygon(dens, col = "steelblue")

Infos

This analysis has been performed using R statistical software (ver. 3.2.4).

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