# Fit Smooth Curve to Plot of Data in R (Example)

In this tutorial you’ll learn how to draw a smooth line to a scatterplot in the R programming language.

Here’s how to do it:

## Introduction of Example Data

The following data is used as basement for this R programming tutorial:

```set.seed(87564832) # Create example data x <- 1:100 y <- sort(rnorm(100))```

The previous output of the RStudio console shows the structure of our example data. It consists of two numeric vectors each containing 100 values.

Now, we can draw our data as follows:

`plot(x, y) # Plot without line` Figure 1 visualizes the output of the previous R syntax: A scatterplot showing our data. However, this scatterplot does not show a fitted curve yet…

## Example 1: Creating Scatterplot with Fitted Smooth Line Using Base R

The following R code explains how to draw a fitted curve to our example plot. Have a look at the following R code:

`curve_values <- loess(y ~ x) # Apply loess function`
```plot(x, y) # Plot with line lines(predict(curve_values), col = "red", lwd = 3)``` As shown in Figure 2, we created a scatterplot with a fitted curve with the previous R code.

## Example 2: Creating Scatterplot with Fitted Smooth Line Using ggplot2 Package

Alternatively to Base R (as explained in Example 1), we can also use the ggplot2 package to draw a scatterplot with a fitted curve.

For this, we first have to store our data vectors in a data frame object as shown below:

```data_ggp <- data.frame(x, y) # Store values in data frame head(data_ggp) # x y # 1 1 -2.813293 # 2 2 -2.502170 # 3 3 -2.297299 # 4 4 -1.934714 # 5 5 -1.875186 # 6 6 -1.816849```

Furthermore, we have to install and load the ggplot2 package:

```install.packages("ggplot2") # Install & load ggplot2 library("ggplot2")```

Next, we can use the geom_smooth function to add a fitted curve on top of our scatterplot as shown below:

```ggplot(data_ggp, aes(x, y)) + # Draw ggplot2 scatterplot with smooth curve geom_point() + geom_smooth(se = FALSE, method = "loess", formula = y ~ x)``` The previously shown figure visualizes the output of the previous R code – A ggplot2 scatterplot with smooth curve on top.

## Video & Further Resources

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Furthermore, you may have a look at the related R tutorials of my website. Some posts are shown below.