title: Closest date in a vector to a given date
body: <p>I would like to identify the closest date in a vector of given date. Let's say I have the following date vector (with 5 random dates): </p>
  
  <pre><code>coldate= as.Date(c("2013-08-03", "2013-09-04", "2013-09-08", "2013-09-12", "2013-11-01"));
  </code></pre>
  
  <p>Now, I want to find the closest date to <code>x = as.Date("2013-10-01")</code> inside this vector. </p>
  
  <p>Here is my code : </p>
  
  <pre><code>&gt; which((coldate-x) == min(coldate-x))
    [1] 1
  </code></pre>
  
  <p>The result should be 4, since the date <code>"2013-09-12"</code> is the closest. But, I have 1... What's wrong in my code?</p>