title: Why is the correlation one when values differ?
body: <p>I have a dataframe <code>book_matrix</code> with users as rows, books as columns, and ratings as values. When I use <code>corrwith()</code> to compute the correlation between 'The Lord of the Rings' and 'The Silmarillion' the result is <code>1.0</code>, but the values are clearly different.</p>
  <p><a href="https://i.stack.imgur.com/VIxJ8.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/VIxJ8.png" alt="enter image description here" /></a></p>
  <p>The non-null values [10, 3] and [10, 9] have correlation <code>1.0</code>. I would expect them to be exactly the same when the correlation is equal to one. How can this happen?</p>