title: Identify binary columns
body: <p>I would like to identify binary columns in a data.frame.</p>
  
  <p>For example, this table</p>
  
  <pre><code>my.table &lt;-read.table(text="a,b,c
  0,2,0
  0.25,1,1
  1,0,0", header=TRUE, as.is=TRUE,sep = ",")
  </code></pre>
  
  <p>would give <code>FALSE, FALSE, TRUE</code></p>