title: python pandas: Remove duplicates by columns A, which is not satisfying a condition in column B
body: <p>I have a dataframe with repeat values in column A. I want to drop duplicates, keeping the row which has its value &gt; 0 in column B</p>
  <p>So this:</p>
  <pre><code>A B
  1 20
  1 10
  1 -3
  2 30
  2 -9
  2 40
  3 10
  </code></pre>
  <p>Should turn into this:</p>
  <pre><code>A B
  1 20
  1 10
  2 30
  2 40
  3 10
  </code></pre>
  <p>Any suggestions on how this can be achieved? I shall be grateful!</p>