title: R pairwise product
body: <p>I'm trying to get the pairwise products of a vector, say</p>
  
  <pre><code>a = c(1,2,3,4)
  </code></pre>
  
  <p>What I'm trying to get is </p>
  
  <p>2,3,4,6,8,12 (in that order).</p>
  
  <p>I've tried using outer:</p>
  
  <pre><code>outer(1:4,2:4)
  </code></pre>
  
  <p>and that gives me a matrix that includes the products I want but I'm not sure how to extract them from the matrix in a way that scales to vectors of higher dimensions.</p>
  
  <p>Thanks!</p>