title: Combine multiple columns into 1 column [python,pandas]
body: <p>I have a pandas data frame with 2 columns: 
  <code>{'A':[1, 2, 3],'B':[4, 5, 6]}</code></p>
  
  <p>I want to create a new column where:
  <code>{'C':[1 4,2 5,3 6]}</code></p>