A legend is an essential feature of a plot that allows you to distinguish between different groups represented in the plot. It explains the meanings of the symbols, colors, and shapes used in the plot. In R, the position of a legend can be changed using various methods. This article will give a detailed walkthrough of how to adjust the legend’s position in base R plots to enhance the readability and clarity of your visualizations.
Understanding Legends in R
In R, the legend() function allows you to add legends to your plots. The primary arguments to this function are:
- x, y: coordinates to place the legend
- legend: a character vector with the items to appear in the legend
- col: a vector of colors for the legend
- pch: a vector of plotting characters or symbols to be used in the legend
- lty, lwd: line types and widths for lines appearing in the legend
To understand how to position a legend, it’s crucial to understand how to add a legend to a plot. Let’s create a simple plot with a legend:
# Plot
plot(1:10, rnorm(10), pch=16, col="red", main="Plot with Legend")
legend("topright", legend="Random Data", col="red", pch=16)
In the above code, we first create a scatterplot of 10 random numbers, with the points marked with filled circles (pch=16) in red color. We then add a legend in the top-right corner (indicated by “topright”) with the label “Random Data”.
Changing the Legend Position in Base R Plots
The legend() function in R uses the x and y parameters to specify the position of the legend. You can use the predefined positions, or you can specify the exact coordinates where the legend should be placed.
1. Using Predefined Positions
The most common method to specify the legend position is by using the predefined keywords:
- “bottomright”, “bottom”, “bottomleft”, “left”, “topleft”, “top”, “topright”, “right”, “center”
Each of these keywords places the legend at the corresponding location in the plot. For example:
# Plot
plot(1:10, rnorm(10), pch=16, col="red", main="Plot with Legend")
# Legend at the bottom
legend("bottom", legend="Random Data", col="red", pch=16)
2. Using Exact Coordinates
You can also specify the exact coordinates where you want the legend to be placed. This method provides you with more control over the legend position. You specify the x and y coordinates of the position of the legend in the form legend(x, y, ...). For example:
# Plot
plot(1:10, rnorm(10), pch=16, col="red", main="Plot with Legend")
# Legend at exact position
legend(5, 0, legend="Random Data", col="red", pch=16)
In this example, the legend will be placed at the point (5,0) in the plot.
3. Using Relative Coordinates
R also allows you to specify the position of the legend using relative coordinates in the inset argument. These coordinates are expressed as fractions of the plot region size:
# Plot
plot(1:10, rnorm(10), pch=16, col="red", main="Plot with Legend")
# Legend with inset
legend("topleft", legend="Random Data", col="red", pch=16, inset=c(-0.2,0))
Here, the inset=c(-0.2,0) moves the legend to the left by 20% of the plot region size.
Conclusion
In this article, we discussed how to change the position of a legend in base R plots. The legend() function in R provides several ways to control the position of the legend, from using predefined locations to specifying exact or relative coordinates. Understanding how to adjust the position of a legend in a plot is crucial for creating clear and easy-to-understand visualizations.