title: Extract Consecutive Pairs of Elements from a Vector and Place in a Matrix
body: <p>This may be a simple question but I can not find how to produce pairs of values from a vector sequentially which each pair includes last value and new value in a matrix of values with two columns. Example below</p>
  
  <pre><code>C&lt;-c(1 , 20 , 44 , 62 , 64 , 89 , 91, 100)
  </code></pre>
  
  <p>matrix example</p>
  
  <pre><code>newpairs
       [,1] [,2]
  [1,]    1   20
  [2,]   20   44
  [3,]   44   64
  [4,]   64   89
  [5,]   89   91
  [6,]   91  100
  </code></pre>
  
  <p>So when I try the matrix it does not work as last element is not repated with the new element  </p>
  
  <pre><code>newpairs &lt;- matrix(C, ncol=2, byrow=TRUE) 
  
  newpairs
  
       [,1] [,2]
  [1,]    1   20
  [2,]   44   62
  [3,]   64   89
  [4,]   91  100
  </code></pre>
  
  <p>I guess you can subset but if C values change then you have to change the drop or keep of subset. I also have tried on functions that extract certain increments or that can extract every nth elemen. However I would like to find a systematic way to create the first example matrix. </p>
  
  <p>Any help is welcomed</p>