title: matrix row merge in R
body: <p>I have a matrix </p>
  
  <pre><code>     [,1]   [,2]
   [1,]   2     3
   [2,]   3     5
   [3,]   7     9
   [4,]   11    3
   [5,]   11    8
  </code></pre>
  
  <p>and I want to merge row 1 2 4 5 by their common value.</p>
  
  <p>the result should be output </p>
  
  <pre><code>  2 3 5 11 8
  </code></pre>