title: How can I remove non numeric values for colMeans() function in R?
body: <p>This is the line,</p>
  
  <pre><code>colMeans3 &lt;- colMeans(grade3, na.rm=TRUE)
  </code></pre>
  
  <p>and R says</p>
  
  <pre><code>Error in colMeans(grades3, na.rm = TRUE) : 'x' must be numeric
  </code></pre>