# Set Legend Alpha of ggplot2 Plot in R (Example)

In this R tutorial youâ€™ll learn how to adjust the transparency of ggplot2 legend items.

The article consists of one example for the modification of alpha values. More precisely, the tutorial looks as follows:

Letâ€™s dive right into the R syntax.

## Example Data, Add-On Packages & Default Graphic

As a first step, we have to create some data that we can use in the following examples:

```data <- data.frame(x = 1:10,                     # Create example data
y = 10:1,
group = LETTERS[1:5])
data                                             # Print data
#     x  y group
# 1   1 10     A
# 2   2  9     B
# 3   3  8     C
# 4   4  7     D
# 5   5  6     E
# 6   6  5     A
# 7   7  4     B
# 8   8  3     C
# 9   9  2     D
# 10 10  1     E```

Have a look at the previous RStudio console output. It shows that our exemplifying data consists of ten rows and three columns. The variables x and y contain some numeric values and the variable group specifies the groups of our data points.

For the examples of this tutorial, weâ€™ll also need to install and load the ggplot2 package.

```install.packages("ggplot2")                      # Install ggplot2 package

Now, we can draw our data with default legend items as follows.

```ggp <- ggplot(data, aes(x, y, col = group)) +    # Example plot
geom_point()
ggp                                              # Draw plot```

As shown in Figure 1, the previous R programming syntax plotted a ggplot2 scatterplot with solid legend items (i.e. default alpha value).

## Example: Modifying Legend Alpha of ggplot2 Plot

The following R syntax illustrates how to decrease the alpha (i.e. to increase transparency) of our legend symbols. For this, we have to change the alpha value within the guide_legend function. Have a look at the following R code and the resulting graph:

```ggp +                                            # Adjust alpha argument
guides(colour = guide_legend(override.aes = list(alpha = 0.2)))```

The output of the previous R programming syntax is shown in Figure 2: It shows our ggplot2 graphic with transparent legend symbols.

## Video & Further Resources

If you need further info on the R programming codes of this tutorial, you might want to have a look at the following video of my YouTube channel. In the video, Iâ€™m showing the R codes of this tutorial.

In addition, I can recommend to read the other tutorials of my website. You can find some posts here.

In summary: At this point you should have learned how to increase or decrease the legend alpha of ggplot2 plots in the R programming language. In case you have further questions, please let me know in the comments below.

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