title: Pandas, how to combine multiple columns into an array column
body: <p>I need to put a combined column as the concat of all values of the row.</p>
  
  <p>Source:</p>
  
  <pre><code>pd.DataFrame(data={
      'a' : [1,2,3],
      'b' : [2,3,4]
  })
  </code></pre>
  
  <p>Target:</p>
  
  <pre><code>pd.DataFrame(data={
      'a' : [1,2,3],
      'b' : [2,3,4],
      'combine' : [[1,2],[2,3],[3,4]]
  })
  </code></pre>
  
  <p>Current solution:</p>
  
  <pre><code>test['combine'] = test[['a','b']].apply(lambda x: pd.Series([x.values]), axis=1)
  </code></pre>
  
  <p>Issues:
  I actually have many columns, it seems taking too long to run. Is it a better way.</p>