title: Error in R with t.test (not enough x observations)
body: <p>I've been trying to do some t.test's in R, but something odd is happening.
  When I run the following:</p>
  
  <pre><code>t.test(mean_rts$rt[mean_rts$task=='simonC' &amp; mean_rts$urg=='high'], mean_rts$rt[mean_rts$task=='simonC' &amp; mean_rts$urg=='low'], paired=TRUE)
  </code></pre>
  
  <p>I get an error, namely:</p>
  
  <blockquote>
    <p>Error in t.test.default(mean_rts$rt[mean_rts$task == "simonC" &amp;
    mean_rts$urg ==  : not enough 'x' observations</p>
  </blockquote>
  
  <p>However, I ran t.test before that was the exact same but instead had simonI instead of simonC (including the amount of observations) and that worked perfectly. </p>
  
  <p>Does anyone understand why I am getting this error even though there are the same amount of observations as in a previous t.test that did work?</p>
  
  <p>Also, there are no n.a. values.</p>