R now will keep children away from drugs

June 16, 2014
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(This article was first published on Rexamine » Blog/R-bloggers, and kindly contributed to R-bloggers)

Do you find this plot fancy? If yes, you can find the code at the end of this article BUT if you spend a little time to read it thoroughly, you can learn how to create better ones.

We would like to encourage you and your children (or children you teach) to use our new R package – TurtleGraphics!

TurtleGraphics package offers R-users functionality of the “turtle graphics” from Logo educational programming language. The main idea standing behind it is to inspire the children to learn programming and show that working with computer can be entertaining and creative.

It is very elementary, clear and requires basic algorithm thinking skills, that even children are able to form them. You can learn it in just five short steps.

  • turtle_init() – To start the program call the turtle_init() function. It creates a plot region (called “Terrarium”) and places the Turtle in the middle pointing north.
library(TurtleGraphics)
turtle_init()

  • turtle_forward() and turtle_backward() – Argument to these functions is the distance you desire the Turtle to move. For example, to move the Turtle forward for a distance of 10 units use the turtle_forward() function. To move the Turtle backwards you can use the turtle_backward() function.
turtle_forward(dist=15)

  • turtle_turn()turtle_right() and turtle_left(). They change the Turtle's direction by a given angle.
turtle_right(angle=30)

  • turtle_up() and turtle_down() – To disable the path from being drawn you can simply use the turtle_up() function. Let's consider a simple example. We use the turtle_up() function. Now, when you move forward the path is not visible. If you want the path to be drawn again you should call the turtle_down() function.
turtle_up()
turtle_forward(dist=10)
turtle_down()
turtle_forward(dist=10)

  • turtle_show() and turtle_hide() – Similarly, you may show or hide the Turtle image, using the turtle_show() and turtle_hide() functions respectively. If you call a lot of functions it is strongly recommended to hide the Turtle first as it speeds up the process.
turtle_hide()

These were just the basics of the package. Below we show you the true potential of it:

  turtle_star <- function(intensity=1){
  y <- sample(1:657, 360*intensity, replace=TRUE)
  for (i in 1:(360*intensity)){
  turtle_right(90)
  turtle_col(colors()[y[i]])
  x <- sample(1:100,1)
  turtle_forward(x)
  turtle_up()
  turtle_backward(x)
  turtle_down()
  turtle_left(90)
  turtle_forward(1/intensity)
  turtle_left(1/intensity)
  }}
  turtle_init(500,500)
  turtle_left(90)
  turtle_do({
  turtle_star(7)
  })

One may wonder what turtle_do() function is doing here. It is an advanced way to use the package. The turtle_do() function is designed to call more complicated plot expressions, because it automatically hides the Turtle before starting the operations that results in a faster proceed of plotting.

  drawTriangle<- function(points){
  turtle_setpos(points[1,1],points[1,2])
  turtle_goto(points[2,1],points[2,2])
  turtle_goto(points[3,1],points[3,2])
  turtle_goto(points[1,1],points[1,2])
  }
  getMid<- function(p1,p2) c((p1[1]+p2[1])/2, c(p1[2]+p2[2])/2)
  sierpinski <- function(points, degree){
  drawTriangle(points)
  if (degree  > 0){
  p1 <- matrix(c(points[1,], getMid(points[1,], points[2,]),
  getMid(points[1,], points[3,])), nrow=3, byrow=TRUE)

  sierpinski(p1, degree-1)
  p2 <- matrix(c(points[2,], getMid(points[1,], points[2,]),
  getMid(points[2,], points[3,])), nrow=3, byrow=TRUE)

  sierpinski(p2, degree-1)
  p3 <- matrix(c(points[3,], getMid(points[3,], points[2,]),
  getMid(points[1,], points[3,])), nrow=3, byrow=TRUE)
  sierpinski(p3, degree-1)
  }
  invisible(NULL)
  }
  turtle_init(520, 500, "clip")
  p <- matrix(c(10, 10, 510, 10, 250, 448), nrow=3, byrow=TRUE)
  turtle_col("red")
  turtle_do(sierpinski(p, 6))
  turtle_setpos(250, 448)

We kindly invite you to use TurtleGraphics! Enjoy!
A full tutorial of this package is available here.

Marcin Kosinski, m[email protected]
Natalia Potocka, [email protected]

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