title: In R, how can I reproduce and increase paired values in a vector?
body: <p>In R, I need to create a vector in which the values appear in order, starting with 1, in which each value is duplicated once, as shown below:
  <code>v &lt;- c(1,1,2,2,3,3,4,4,5,5)</code> and so on.</p>
  
  <p>The above vector has five pairs, but the number of pairs can be many more.</p>
  
  <p>How can I do that without having to manually type every pair?</p>