title: How to expand.grid with string elements (the half!)
body: <p>I have the following result of expand grid:</p>
  
  <blockquote>
    <p>d &lt;- expand.grid(c("x","y","z"),c("x","y","z"))</p>
  </blockquote>
  
  <p>Note the vector could be longer than 3 and string length
  could be greater or of different pattern?</p>
  
  <p>What I want is to create a combination of strings
  but only the half of the all combinations:</p>
  
  <pre><code>  Var1 Var2
  1    x    x
  2    y    x
  3    y    y
  4    z    y
  5    x    z
  6    z    z
  </code></pre>