# Add Color Between Two Points of Kernel Density Plot in R (Example)

In this tutorial, I’ll show how to **add color to a certain area below a density plot** in the R programming language.

The content of the post looks as follows:

- Introducing Example Data
- Example: Coloring Particular Area Below Density Plot
- Video & Further Resources

You’re here for the answer, so let’s get straight to the examples!

## Introducing Example Data

First, we need to generate some random data that we can draw as kernel density plot later on:

set.seed(75757) # Create example data x <- rnorm(1000) |

set.seed(75757) # Create example data x <- rnorm(1000)

Our example data consists of 1000 numeric values and is normally distributed.

Now, we can convert our numeric vector to a density object with the density function:

dens_x <- density(x) # Compute density of data |

dens_x <- density(x) # Compute density of data

We can draw a graph with default specifications by using the plot function:

plot(dens_x) # Default plot of density |

plot(dens_x) # Default plot of density

**Figure 1: Basic Density Plot in R.**

Figure 1 shows how our example plot looks like. It’s a normally distributed kernel density graph with a mean of 0 and a standard deviation of 1.

Let’s add some color…

## Example: Coloring Particular Area Below Density Plot

If we want to add some color or a shade below our kernel density plot, we first need to specify between which points on the x-axis we want to add this color. In this example, we are using the lower limit – 0.5 and the upper limit 1:

x_low <- min(which(dens_x$x >= - 0.5)) # Define lower limit of colored area x_high <- max(which(dens_x$x < 1)) # Define upper limit of colored area |

x_low <- min(which(dens_x$x >= - 0.5)) # Define lower limit of colored area x_high <- max(which(dens_x$x < 1)) # Define upper limit of colored area

Now, we can use the with and the polygon functions to add some color between our two limits:

with(dens_x, # Add color between two limits polygon(x = c(x[c(x_low, x_low:x_high, x_high)]), y = c(0, y[x_low:x_high], 0), col = "#1b98e0")) |

with(dens_x, # Add color between two limits polygon(x = c(x[c(x_low, x_low:x_high, x_high)]), y = c(0, y[x_low:x_high], 0), col = "#1b98e0"))

**Figure 2: Density with Colored Area Between Two Points.**

Figure 2 illustrates the output of the previous R programming code. As you can see, we added some blue color below the previously specified area of our graphic.

## Video & Further Resources

Do you want to learn more about graphics in R? Then you might want to watch the following video which I have published on my YouTube channel. In the video, I show the R programming code of this page.

*The YouTube video will be added soon.*

Furthermore, you may have a look at this forum thread at Stack Overflow. The R code shown in this tread was used as basement for this tutorial and in the thread you can also find R programming codes for the coloring of certain areas below a density based on the ggplot2 package.

In addition, you may want to have a look at some of the related articles on my website. You can find a selection of articles below:

Summary: You learned in this tutorial how to **shade a particular part of a kernel density graphic** in the R programming language. Let me know in the comments, if you have any additional questions.

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