title: Add unit labels to radar plot and remove outer ring ggplot2 (spider web plot, coord_radar)
body: <p>I've been working on a radar plot recently and found a great bit of code on from <a href="http://www.cmap.polytechnique.fr/~lepennec/R/Radar/RadarAndParallelPlots.html" rel="nofollow noreferrer">Erwan Le Pennec</a>. I've made a few edits, however there are some parts I couldn't work out how to remove the outermost circle as it doesn't define a value. Currently the code is plotting the major grid lines. I've tried to trick it into removing both axis and only plotting the minor increments however either has worked. </p>
  
  <p>Cheers!</p>
  
  <p>Here is my code:</p>
  
  <pre><code>coord_radar &lt;- function (theta = "x", start = 0, direction = 1) 
  
  
   {
          theta &lt;- match.arg(theta, c("x", "y"))
          r &lt;- if (theta == "x") 
              "y"
          else "x"
          ggproto("CordRadar", CoordPolar, theta = theta, r = r, start = start, 
              direction = sign(direction),
              is_linear = function(coord) TRUE)
      }
  
  RadarTheme&lt;-theme(panel.background=element_blank(),
                        plot.title= element_text(size = 25,face=c("bold","italic")),
                        plot.margin = unit(c(2, 2, 2, 2), "cm"),
                        text=element_text(family="Open Sans"), aspect.ratio = 1,
                        legend.position="bottom",legend.title=element_blank(),legend.direction="vertical",
                        strip.text.x = element_text(size = rel(0.8)),
                        axis.text.x = element_text(size = 15,face ="bold"),
                        axis.ticks.y = element_blank(),
                        axis.text.y = element_blank(),
                        axis.line.x=element_line(size=0.5),
                        panel.grid.major=element_line(size=0.3,linetype = 2,colour="grey"))
  
      mtcarsscaled &lt;- as.data.frame(lapply(mtcars, ggplot2:::rescale01))
      mtcarsscaled$model &lt;- rownames(mtcars)
  
      mtcarsscaled1&lt;-subset(mtcarsscaled,model=="Lotus Europa")
      mtcarsscaled2&lt;-subset(mtcarsscaled,model=="Volvo 142E")
      mtcarsscaled&lt;-rbind(mtcarsscaled1,mtcarsscaled2)
  
      mtcarsmelted &lt;- reshape2::melt(mtcarsscaled)
      mtcarsmelted$value&lt;-mtcarsmelted$value*100
      c&lt;-ggplot(mtcarsmelted, aes(x = variable, y = value)) +
        geom_polygon(aes(group = model, color = model,fill = model),alpha=0.4, size = 1, show.legend = TRUE) +
        RadarTheme+
        xlab("") + ylab("") +scale_y_continuous(limits = c(-5, 100), breaks = seq(0, 100, 25))+
        coord_radar()+
        guides(fill = guide_legend(keywidth = rel(1.3), keyheight = rel(1.3)))
      print(c)
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/FZfeL.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/FZfeL.png" alt="Stuff to change"></a></p>