title: How to merge two rows with the same value in a given column
body: <p>Hey I have a DataFrame like this:</p>
  <pre><code>d =  {&quot;KEY&quot;: [&quot;KEY2&quot;, &quot;KEY2&quot;], &quot;String value&quot;: [&quot;value 1&quot;, &quot;value 2&quot;], &quot;list value&quot;: [[&quot;val1&quot;], [&quot;val2&quot;]]}
  df = pd.DataFrame(d)
  df
  </code></pre>
  <p>In <code>KEY</code> column there is the same value in both rows. What I want to do is to create one row from this two rows (or more in my DataFrame) in such a way that values from from a given columns (except <code>KEY</code> and possibly one more column) are added. So finally I want sth like this:</p>
  <pre><code>d2 = {&quot;KEY&quot;: [&quot;KEY2&quot;], &quot;String value&quot;: [&quot;value 1&quot; + &quot;value 2&quot;], &quot;list value&quot;: [[&quot;val1&quot;] + [&quot;val2&quot;]]}
  res = pd.DataFrame(d2)
  res
  </code></pre>
  <p>How can I do that?</p>