Understanding Different Plotting Characters in R
Introduction
The pch parameter in R’s plot() function is used to specify a plotting character. This parameter can significantly impact the appearance of a plot, especially when multiple lines need to be plotted with different characters. In this article, we will delve into the world of plotting characters, explore how they work, and discuss their usage.
What are Plotting Characters?
In R’s graphics system, plotting characters refer to the symbols or markers used to represent data points on a graph. These characters can range from simple dots (.) to complex shapes like triangles (3), stars (*), and more. The choice of plotting character can significantly affect the aesthetic appeal of a plot.
Default Plotting Character
When no pch value is specified, R defaults to using the “l” character, which represents a line. This means that if you simply call plot() without specifying any characters, it will plot your data as a solid line.
# Create some sample data
x <- 1:10
y <- runif(10)
# Plot the data with default plotting character (line)
plot(x, y)
Changing the Plotting Character
To change the plotting character, you can use the pch parameter in the plot() function. The value of pch must be a valid plotting character code.
# Create some sample data
x <- 1:10
y <- runif(10)
# Plot the data with custom plotting characters
plot(x, y, pch = c(1, 2, 3, 4, 5))
In this example, we’ve plotted three lines with different plotting characters.
Using Different Plotting Characters for Multiple Lines
However, when using multiple lines() calls to plot separate lines on the same graph, things become more complicated. As we’ll discuss in the next section, the default plotting character used by lines() ignores the pch value specified in the individual line plots.
The Problem with Using Different Plotting Characters
When you call plot() multiple times with different values of pch, each plot is drawn on top of the previous one. However, when you use lines(), R defaults to using a single plotting character code for all lines combined. This means that even if you specify different values of pch for individual line plots, they will all be displayed using the same plotting character.
The Solution: Specifying the Plotting Character with lines()
To avoid this issue, you need to explicitly specify the plotting character for each line plot using the type parameter in lines(). Here are some valid values:
l: Line (default)b: Line (filled polygon)o: Line (open circle)p: Points: Square
# Create some sample data
x <- 1:10
y <- runif(10)
# Plot the first line with default plotting character (line)
plot(x, y, pch = 3)
# Plot the second line with custom plotting characters
lines(x, y, type = "o")
# Plot the third line with different plotting characters
lines(x, y, pch = c(2, 4, 5), type = "b")
In this example, we’ve plotted three lines using different values of type in lines(). The first line is a solid line with default plotting character (l), while the second and third lines have custom plotting characters.
Example: Plotting Multiple Lines with Different Characters
Let’s create an example where we plot multiple lines with different plotting characters:
# Create some sample data
x <- 1:10
y1 <- runif(10)
y2 <- runif(10, min = 0.3, max = 0.7)
y3 <- runif(10)
# Plot the first line with default plotting character (line)
plot(x, y1, pch = 3)
# Plot the second line with custom plotting characters
lines(x, y2, type = "o")
# Plot the third line with different plotting characters
lines(x, y3, pch = c(2, 4, 5), type = "b")
In this example, we’ve plotted three lines with different values of type in lines(). The first line is a solid line with default plotting character (l), while the second and third lines have custom plotting characters.
Conclusion
Plotting characters play an essential role in customizing the appearance of plots in R. By understanding how to use these characters effectively, you can create visually appealing plots that convey your message clearly.
Last modified on 2024-08-11