title: 'x' must be a numeric vector: Error from data.frame of numbers
body: <p>I am running a cor.test on two columns within a file/table.  </p>
  
  <pre><code>tmp &lt;- read.table(files_to_test[i], header=TRUE, sep="\t")
  ## Obtain Columns To Compare ##
  colA &lt;-tmp[compareA]
  colB &lt;-tmp[compareB]
  # sctr = 'spearman cor.test result'
  sctr &lt;- cor.test(colA, colB, alternative="two.sided", method="spearman")
  </code></pre>
  
  <p>But I am getting this confounding error...</p>
  
  <pre><code>Error in cor.test.default(colA, colB, alternative = "two.sided", method = "spearman") : 
  'x' must be a numeric vector
  </code></pre>
  
  <p>the values in the columns ARE numbers but</p>
  
  <pre><code>is.numeric(colA) = FALSE 
  class (colA) = data.frame
  </code></pre>
  
  <p>What have I missed?</p>