title: plot count of values by factor in ggplot
body: <p>New to R, stuck googling this (probably easy) thing for too long.</p>
  
  <p>I want to plot the proportion of males that fathered offspring, according to whether they have a nest or not. (I don't want the information of how many offspring they fathered). This is my dataset called "males"</p>
  
  <pre><code>fishID nest off
  fish1    1  25
  fish2    0   0
  fish3    0   5
  fish4    1  15
  fish5    1   0
  fish6    0   2
  fish7    0   0
  fish8    1   4
  </code></pre>
  
  <p>I've used the following code to change the values of offspring to 0 and 1 (though this feels clumsy already)...</p>
  
  <pre><code>#converts the values in offspring to 0 and 1s
  vars=c("off")
  males[males$off != "0", vars]="1"
  males 
  </code></pre>
  
  <p>...and I can plot proportions using...</p>
  
  <pre><code>ggplot(males,aes(x = males$nest,fill = males$off)) + 
  geom_bar(position = "fill")
  </code></pre>
  
  <p>...but I would like to colour them so that 0 (no nest) is one colour and 1 (nest) is another colour, then the proportion of males that didn't father offspring is a paler version of each colour. The above produces colours according to "offspring", irrespective of "nest".</p>
  
  <p>Tips welcome.
   (Mac OS X, R 3.0.3 GUI 1.63 Snow Leopard build (6660))</p>