title: Two paired t-test p-value = NA and t=NaN
body: <p>I would like to do the following paired t-test:</p>
  
  <pre><code>str1&lt;-' ENSEMBLE 0.934 0.934 0.934 0.934 '
    str2&lt;-' J48 0.934 0.934 0.934 0.934 '
  
    df1 &lt;- read.table(text=scan(text=str1, what='', quiet=TRUE), header=TRUE)
    df2 &lt;- read.table(text=scan(text=str2, what='', quiet=TRUE), header=TRUE)
  
  t.test ( df1$ENSEMBLE, df2$J48, mu=0 , alt="two.sided", paired = T, conf.level = 0.95)
  </code></pre>
  
  <p>I get the following result:</p>
  
  <pre><code>Paired t-test
  
  data:  df1$ENSEMBLE and df2$J48
  t = NaN, df = 3, p-value = NA
  alternative hypothesis: true difference in means is not equal to 0
  95 percent confidence interval:
   NaN NaN
  sample estimates:
  mean of the differences 
                        0 
  </code></pre>
  
  <p>Why do I get it?</p>