title: performing ccf on time series- univariate problems
body: <p>I have two xts objects, rest and awake.</p>
  
  <p>I want to cross correlate them, so I do</p>
  
  <pre><code>ccf(rest, awake)
  </code></pre>
  
  <p>But I get the message </p>
  
  <pre><code>Error in ccf(rest, awake) : univariate time series only
  </code></pre>
  
  <p>awake looks like this but 264 rows.</p>
  
  <pre><code>2017-01-01 07:50:00    94.44444
  2017-01-02 08:05:00    95.43147
  </code></pre>
  
  <p>rest is similar, with 264 rows.</p>
  
  <pre><code>2017-01-01    57
  2017-01-02    58
  </code></pre>
  
  <p>Why is it throwing this error?  I've tried removing the hours/minutes/seconds from awake, but that doesn't work either.  What am I missing?</p>