Turtle graphics is a classic teaching tool in computer science, originally invented in the 1960s and reimplemented over and over again in different programming languages. In R, there is a similar package called TurtleGraphics:

install.packages('TurtleGraphics')
library(TurtleGraphics)

Here’s the idea. You have a turtle, and she lives in a nice warm terrarium. The terrarium is 100 x 100 units in size, where the lower-left corner is at the (x, y) position of (0, 0). When you call turtle_init(), the turtle is initially positioned in the center of the terrarium at (50, 50):

turtle_init()

You can move the turtle using a variety of movement functions (see ?turtle_move()), and she will leave a trail where ever she goes. For example, you can move her 10 units forward from her starting position:

turtle_init()
turtle_forward(distance = 10)

You can also make the turtle jump to a new position (without drawing a line) by using the turtle_setpos(x, y), where (x, y) is a coordinate within the 100 x 100 terrarium:

turtle_init()
turtle_setpos(x=10, y=10)

Simple enough, right? But what if I want my turtle to draw a more complicated shape? Let’s say I want her to draw a hexagon. There are six sides to the hexagon, so the most natural way to write code for this is to write a for loop that loops over the sides! At each iteration within the loop, I’ll have the turtle walk forwards, and then turn 60 degrees to the left. Here’s what happens:

turtle_init()
for (side in 1:6) {
turtle_forward(distance = 10)
turtle_left(angle = 60)
}

Cool! As you draw more complex shapes, you can speed up the process by wrapping your turtle commands inside the turtle_do({}) function. This will skip the animations of the turtle moving and will jump straight to the final position. For example, here’s the hexagon again without animations:

turtle_init()
turtle_do({
for (side in 1:6) {
turtle_forward(distance = 10)
turtle_left(angle = 60)
}
})

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EMSE 6574, Sec. 11: Programming for Analytics (Fall 2019)
George Washington University | School of Engineering & Applied Science
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