title: Pandas duplicates when grouped
body: <pre><code>x = df.groupby(["Customer ID", "Category"]).sum().sort_values(by="VALUE", ascending=False)
  </code></pre>
  
  <p>I want to group by Customer ID but when I use above code, it duplicates customers...</p>
  
  <p>Here is the result:</p>
  
  <p><a href="https://i.stack.imgur.com/y4UDn.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/y4UDn.png" alt="Image"></a></p>
  
  <p>Source DF:</p>
  
  <pre><code>  Customer ID Category  Value
  0           A        x      5
  1           B        y      5
  2           B        z      6
  3           C        x      7
  4           A        z      2
  5           B        x      5
  6           A        x      1
  </code></pre>
  
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