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Adam Spannbauer
Adam Spannbauer

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OOP Fractal Trees in R with R6, ggplot2, & gganimate (part 2)

This post is part 2 of 2, and, as stated in part 1, the end goal is to create an animated fractal tree with R6 & gganimate. Today, we will be animating the fractal_tree R6 class from part 1 with gganimate.

The below code and plot show where we're going to get by the end of this post.

# Create & animate R6 tree object
tree = fractal_tree_seq$new()

Note: This post is meant to explore R6 functionality; it's not claiming to be the best way to create our fractal trees. Some design choices were solely to leverage varied features. Additionally, this post is more example-based than explanation based. For more in-depth explanations, I recommend going to this page from R6 or check out this chapter from Advanced R


We already have a fractal_tree object that can create a single tree with branches positioned at a given angle. For simplicity, we will build our animated tree as a sequence of our (already defined) fractal_tree objects; each tree will be a frame in the animation. Disclaimer: if you end up running this code, you'll see that this approach might not be the most efficient approach, but it works.


Note: This post's code assumes that the objects from part 1 are loaded into your R session. The complete code from part 1 can be found here

Sticking with the theme of the 2 part series, we'll create a single R6 class to house our animation process. The "Design" section above might seem to be written at a very high level, but it covers almost all of the implementation details that we'll discuss below.


The object doing the animation is given the name fractal_tree_seq since it is simply a sequence of fractal_trees. In the initialize method of the object, we loop the user provided angle_seq and create a tree at each angle in the sequence. Additionally, when we create each tree, we assign some metadata that shows which frame the tree belongs to. Lastly, in our initialize method we assign a color to each angle, this info will be used in plotting to give our animation some flare.

To wrap up our fractal_tree_seq class we add a public animate method that looks a lot like the plot method from part 1. The syntax of gganimate is very similar to ggplot2's, so experience with the later should make the animate code feel familiar. The only bit of gganimate code we add to the ggplot2 expression is + transition_manual(frame). This command will use the frame data we assigned in initialize to create a gif of our fractal_trees.

And that's it! We achieved the goal of creating and animating a fractal tree with R6 and gganimate.

fractal_tree_seq = R6Class('fractal_tree_seq',
                           public = list(
                             trees = data.frame(),
                             initialize = function(trunk_len = 10,
                                                   angle_seq = seq(0, 2 * pi - pi / 32, pi / 32),
                                                   len_decay = 0.7,
                                                   min_len = 0.25,
                                                   verbose = TRUE) {
                                 total = length(angle_seq)
                                 for (i in seq_along(angle_seq)) {
                                   if (verbose) cat(sprintf('creating tree %s of %s\n', i, total))
                                   angle = angle_seq[i]

                                   tree_i = fractal_tree$new(trunk_len = trunk_len,
                                                             delta_angle = angle,
                                                             len_decay = len_decay,
                                                             min_len = min_len)

                                   branches_i = tree_i$branches
                                   branches_i$angle = angle
                                   branches_i$frame = i

                                   self$trees = rbind(self$trees, branches_i)

                                 angle_colors = data.frame(angle = sort(unique(self$trees$angle)))
                                 angle_colors$angle_color = rainbow(nrow(angle_colors))

                                 self$trees = merge(self$trees, angle_colors, all.x = TRUE, by = 'angle')
                               },  # initialize

                             animate = function() {
                                 ggplot(self$trees, aes(x, y, group = id)) +
                                   geom_line(aes(color = branch_color)) +
                                   geom_point(size = .2, aes(color = angle_color)) +
                                   scale_color_identity() +
                                   guides(color = FALSE, linetype = FALSE) +
                                   theme_void() +
                             )  # public
                           )  #fractal_tree_seq

Final Product

This last section will be a few examples of using the functionality of our fractal_tree class.

# Create & animate R6 tree object
tree = fractal_tree_seq$new()

# Create & animate R6 tree object with new min_len
tree = fractal_tree_seq$new(min_len = 3)

# Create & animate R6 tree object with new angle_seq
tree_seq = fractal_tree_seq$new(angle_seq = runif(4, min=pi / 16, max=pi / 4))

* made smaller since it's so distracting

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