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Introduction

A density plot visualises the distribution of data over a continuous interval (or time period). Density Plots are not affected by the number of bins (each bar used in a typical histogram) used, thus, they are better at visualizing the shape of the distribution than a histogram unless the bins in the histogram have a theoretical meaning.

Keep in Mind

  • Notice that the variable on the x-axis should be continuous. Density plots are not designed for use with discrete variables.

Also Consider

= You might also want to know how to make a histogram or a line graph, click Histogram or Line graph for more information.

Implementations

Python

In this example, we’ll use seaborn, a declarative plotting library that provides a quick and easy way to produce density plots. It builds on matplotlib.

# You may need to install seaborn on the command line using 'pip install seaborn' or 'conda install seaborn'
import seaborn as sns

# Set a theme for seaborn
sns.set_theme(style="darkgrid")

# Load the example diamonds dataset
diamonds = sns.load_dataset("diamonds")

# Take a look at the data
print(diamonds.head())
carat cut color clarity depth table price x y z
0 0.23 Ideal E SI2 61.5 55.0 326 3.95 3.98 2.43
1 0.21 Premium E SI1 59.8 61.0 326 3.89 3.84 2.31
2 0.23 Good E VS1 56.9 65.0 327 4.05 4.07 2.31
3 0.29 Premium I VS2 62.4 58.0 334 4.20 4.23 2.63
4 0.31 Good J SI2 63.3 58.0 335 4.34 4.35 2.75
sns.kdeplot(data=diamonds, x="price", cut=0);

png

This is basic, but there are lots of ways to adjust it through keyword arguments (you can see these by running help(sns.kdeplot)) or via calling functions on the matplotlib ax object that running sns.kdeplot returns when not followed by ;. In this simple example, the cut keyword argument forces the density estimate to end at the end-points of the data–which makes sense for a variable like price, which has a hard cut-off at 0.

Let’s use further keyword arguments to enrich the plot, including different colours (‘hues’) for each cut of diamond. One keyword argument that may not be obvious is hue_order. The default function call would have arranged the cut types so that the ‘Fair’ cut obscured the other types, so the argument passed to the hue_order keyword below reverses the order of the unique list of diamond cuts via [::-1].

sns.kdeplot(data=diamonds,
            x="price",
            hue="cut",
            hue_order=diamonds['cut'].unique()[::-1],
            fill=True,
            alpha=.4,
            linewidth=0.5,
            cut=0.);

png

R

For this R demonstration, we are going to use ggplot2 package to create a density plot. Additionally, we will use the dataset diamonds that is natively available in R.

To begin with this R demonstration, make sure that we install and load all the useful packages that we need it. We use the function p_load() in pacman package to help us to install and load the packages at one time.

#install and load necessary packages
if (!require("pacman")) install.packages("pacman")
pacman::p_load(ggplot2,viridis,RColorBrewer,tidyverse,ggthemes,ggpubr,datasets)

Next, in order to make a density plot, we are going to use the ggplot() and geom_density() functions. We will specify price as our x-axis.


ggplot(diamonds, aes(x=price))+
  geom_density()

Basic density plot

We can always change the color of the density plot using the col argument and fill the color inside the density plot using fill argument. Furthermore, we can specify the degree of transparency density fill area using the argument alpha where alpha ranges from 0 to 1.

ggplot(diamonds, aes(x=price))+
  geom_density(fill="lightblue",
               col='black',
               alpha=0.6)

Colored density plot We can also change the type of line of the density plot as well by adding linetype= inside geom_density().

ggplot(diamonds, aes(x=price))+
  geom_density(fill="lightblue",
               col='black',
               linetype="dashed")

Density plot with linetype Furthermore, you can also combine both histogram and density plots together.

ggplot(diamonds, aes(x=price)) + 
 geom_histogram(aes(y=..density..), colour="black", fill="grey45")+
 geom_density(col="red",size=1,linetype='dashed') 

Density Plot Overlaid on Histogram

What happen if we want to make multiple densities?

For example, we want to make multiple densities plots for price based on the type of cut, all we need to do is adding fill=cut inside aes().

ggplot(data=diamonds, aes(x=price,fill=cut)) +
    geom_density(adjust=1.5, 
                 alpha=.3)

multiple :