Draw a radar chart with ggplot.

ggradar.R

library(tidyverse)

# http://www.cmap.polytechnique.fr/~lepennec/R/Radar/RadarAndParallelPlots.html
coord_radar <- function (theta = "x", start = 0, direction = 1){
  theta <- match.arg(theta, c("x", "y"))
  r <- if (theta == "x") 
    "y"
  else "x"
  ggproto("CordRadar", CoordPolar, theta = theta, r = r, start = start, 
          direction = sign(direction),
          is_linear = function(coord) TRUE)
}

# https://qiita.com/yutannihilation/items/f30baef75a0ac02bb2f0
GeomRadar <- ggproto("GeomRadar", GeomPolygon,
                     default_aes = aes(colour = "black", fill = NA, size = 0.5, linetype = 1, alpha = NA),
                     draw_key = draw_key_path
)
geom_radar <- function(mapping = NULL, data = NULL, stat = "identity",
                       position = "identity", na.rm = FALSE, show.legend = NA, 
                       inherit.aes = TRUE, ...) {
  layer(
    stat = stat, geom = GeomRadar, data = data, mapping = mapping,
    position = position, show.legend = show.legend, inherit.aes = inherit.aes,
    params = list(na.rm = na.rm, ...)
  )
}

n <- 10
m <- 5
dat <- tibble(item = rep(letters[1:n], each = m), 
              index = rep(LETTERS[1:m], n),
              value = runif(n * m))
str(dat)
dat %>% ggplot(aes(x = index, y = value, color = item, group = item)) + 
  geom_radar() + geom_point() + coord_radar() +
  scale_x_discrete(expand = expand_scale(add = c(0, 1))) +
  theme_bw(base_family = "Palatino") + theme(axis.title = element_blank())

 

This was a really helpful bit of code an produced a much better set of figures than other methods I had found.