title: Select column values satisfying multiple conditions in other columns
body: <p>I have a pandas dataframe such as: </p>
  
  <pre><code>    Species     Pathway     Number of Gene Families
  1    uniSU2     ABC           1.0
  2    uniSU2     Wzy           11.0
  3    uniSU2     Synthase      2.0
  4    n116       Wzy           0.0   
  5    n116       ABC           4.0
  7    n116       Synthase      14.0
  8    Aullax     ABC           9.0
  9    Aulax      Synthase      1.0
  10   Aullax     Wzy           2.0
  11   Criepi     Wzy           0.0
  12   Criepi     ABC           2.0
  13   Criepi     Synthase      3.0
  </code></pre>
  
  <p>I want to select the Species (1st column) that have all the three possible pathways - ABC, Wzy, Synthase (2nd column). 
  For this, the Number of Gene Families (3rd column) would have to be a positive number (>0) for all the three pathways -  ABC > 0; Wzy > 0 and Synthase > 0.</p>
  
  <p>The results for this subset of my dataframe would be: </p>
  
  <pre><code>Species 
  uniSU2
  Aullax
  </code></pre>
  
  <p>I think this gets me halfway: </p>
  
  <pre><code>geneCount_stacked.loc[geneCount_stacked['Number of Gene Families'] &gt; 0, ['Species','Pathway']] 
  </code></pre>
  
  <p>But I can't workout how to move forward from here. </p>
  
  <p>Many thanks in advance! </p>