title: R - Corrplot() correlation matrix has question marks in the grid. How to understand the matrix?
body: <p>I am trying to create a correlation matrix of the variables from IMDB movie prediction dataset from kaggle. When I try to plot the correlation matrix I get the following question marks in the matrix. </p>
  
  <p><img src="https://i.stack.imgur.com/slktd.png" alt="Correlation matrix"></p>
  
  <p>All the variables are numeric. How do i understand the question marks?</p>
  
  <pre><code>numeric_col &lt;- sapply(df, is.numeric)
  movie_numeric &lt;- df[, numeric_col]
  Correlation &lt;- cor(movie_numeric)
  corrplot(Correlation)
  </code></pre>