title: Slicing/filtering with non-unique values in index
body: <p>New to python and struggling with a dataset for waste treatment and tonnes from various regions in Norway. My problem is there are many entries from the same municipality depending on how the waste was treated. In other words - i have a index column with non-unique string values. How can I easily find something like tonnes recycled in a specific municipality?</p>
  <p>I've used this to find values from other columns:</p>
  <p>nydf[nydf[&quot;Behandling&quot;]==&quot;Deponi&quot;][&quot;Tonn&quot;].sum()</p>
  <p>But this fails if I try to use the index column &quot;Kommune&quot;:
  nydf[nydf[&quot;Kommune&quot;]==&quot;Hitra&quot;][&quot;Tonn&quot;].sum()</p>
  <p>Dataset imported from Excel looks like this:
  <a href="https://i.stack.imgur.com/1Cw31.png" rel="nofollow noreferrer">enter image description here</a></p>
  <p>I get this error:
  <a href="https://i.stack.imgur.com/tuuIM.png" rel="nofollow noreferrer">enter image description here</a></p>