# geom_christmas_tree(): a new geom for ggplot2 v2.0

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Version 2.0 of the ggplot2 package (on GitHub) has a very nice mechanism for adding new geoms and stats (more about it here).

Christmas are coming, so maybe one would like to make his plots more tree’ish?

Below you will find a definition of *geom_christmas_tree()* geom. It supports following aesthetics: size (number of segments), fill, color, x and y.

With *mpg* data you can plot a colourful forest.

ggplot(mpg, aes(displ, hwy, fill=manufacturer)) + geom_christmas_tree(size=2)

With *iris* dataset you can plot three hills and few trees.

ggplot(iris, aes(x=Sepal.Length, y=Petal.Length)) + stat_density_2d(aes(color=Species)) + geom_christmas_tree(aes(size=Petal.Length, fill=Species)) + theme_void() + theme(legend.position="none")

Here is the full definition of the *geom_christmas_tree()* geom (tested with ggplot2 v2.0).

GeomChristmasTree <- ggproto("GeomChristmasTree", Geom, required_aes = c("x", "y"), default_aes = aes(shape = 19, colour = "black", fill = "green4", size = 3, linetype = 1, alpha = 1, fontsize = 1), draw_key = draw_key_polygon, draw_panel = function(data, panel_scales, coord) { coords <- coord$transform(data, panel_scales) # each tree has 4*branches + 3 points if (length(coords$size) == 1) { tsize <- rep(pmax(1, round(coords$size)), length(coords$x)) theight <- rep(pmax(0, round(coords$size)), length(coords$x)) } else { tsize <- pmax(1, round(coords$size)) theight <- pmax(0, coords$size) } # scale factors r01x <- diff(range(coords$x))/100 r01y <- diff(range(coords$y))/100 # coords longx <- unlist(lapply(seq_along(coords$x), function(i) { if (tsize[i] == 1) { dx <- -c(0.3, 0.3, 1.2, 0, -1.2, -0.3, -0.3) } else { dx <- -c(0.3, 0.3, rep(c(1.2,0.3), tsize[i]-1), 1.2, 0, -1.2, rep(c(-0.3,-1.2), tsize[i]-1), -0.3, -0.3) } r01x*dx + coords$x[i] })) longy <- unlist(lapply(seq_along(coords$y), function(i) { if (tsize[i] == 1) { dy <- c(-0.5, 0, 0, theight[i], 0, 0, -0.5) } else { dy <- c(-0.5, 0, 0, rep(1:(tsize[i]-1), each=2), theight[i], rep((tsize[i]-1):1, each=2), 0, 0, -0.5) } r01y*dy + coords$y[i] })) longid <- unlist(sapply(seq_along(coords$y), function(i) { rep(i, each=4*tsize[i]+3) })) grid::polygonGrob( longx, longy, id = longid, gp = grid::gpar(col = coords[,"colour"], fill = coords[,"fill"], fontsize = 10) ) } ) geom_christmas_tree <- function(mapping = NULL, data = NULL, stat = "identity", position = "identity", na.rm = FALSE, show.legend = NA, inherit.aes = TRUE, ...) { layer( geom = GeomChristmasTree, mapping = mapping, data = data, stat = stat, position = position, show.legend = show.legend, inherit.aes = inherit.aes, params = list(na.rm = na.rm, ...) ) }

Btw: you still have four days to submit your chRistmas tRee.

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