Closing the lines in a ggplot2 radar / spider chart

Question

I need a flexible way to make radar / spider charts in ggplot2. From solutions I\'ve found on github and the ggplot2 group, I\'ve come this far:

library(ggpl         


        

Answer 1

• solution key factor
  1. add duplicated mpg row after melt by rbind
  2. inherit CoordPolar on ggproto
  3. set is_linear = function() TRUE on ggproto

especially is_linear = function() TRUE is important,
since if not you will get plot like this...

with is_linear = function() TRUE settings you can get,

library(dplyr)
library(data.table)
library(ggplot2)

rm(list=ls())

scale_zero_to_one <- 
  function(x) {
    r <- range(x, na.rm = TRUE)
    min <- r[1]
    max <- r[2]
    (x - min) / (max - min)
  }

scaled.data <-
  mtcars %>%
  lapply(scale_zero_to_one) %>%
  as.data.frame %>%
  mutate(car.name=rownames(mtcars)) 

plot.data <-
  scaled.data %>%
  melt(id.vars='car.name') %>%
  rbind(subset(., variable == names(scaled.data)[1]))

# create new coord : inherit coord_polar
coord_radar <- 
  function(theta='x', start=0, direction=1){
    # input parameter sanity check
    match.arg(theta, c('x','y'))

    ggproto(
      NULL, CoordPolar, 
      theta=theta, r=ifelse(theta=='x','y','x'),
      start=start, direction=sign(direction),
      is_linear=function() TRUE)
  }

plot.data %>%
  ggplot(aes(x=variable, y=value, group=car.name, colour=car.name)) + 
  geom_path() +
  geom_point(size=rel(0.9)) +
  coord_radar() + 
  facet_wrap(~ car.name, nrow=4) + 
  theme_bw() +
  theme(
    axis.title.y = element_blank(),
    axis.text.y = element_blank(),
    axis.ticks.y = element_blank(),
    axis.title.x = element_blank(),
    legend.position = 'none') +
  labs(title = "Cars' Status")

• final result