title: Concatenate two dataframes of different sizes (pandas)
body: <p>I have two dataframes with unique <code>id</code>s. They share some columns but not all. I need to create a combined dataframe which will include rows from missing <code>id</code>s from the second dataframe. Tried merge and concat, no luck. It's probably too late, my brain stopped working. Will appreciate your help!</p>
  
  <pre><code>   df1 = pd.DataFrame({
          'id': ['a','b','c','d','f','g','h','j','k','l','m'],
          'metric1': [123,22,356,412,54,634,72,812,129,110,200],
          'metric2':[1,2,3,4,5,6,7,8,9,10,11]
          })
  
  
  df2 = pd.DataFrame({
      'id': ['a','b','c','d','f','g','h','q','z','w'],
      'metric1': [123,22,356,412,54,634,72,812,129,110]
      })
  df2
  </code></pre>
  
  <p>The result should look like this:</p>
  
  <pre><code>    id  metric1 metric2
  0   a   123     1.0
  1   b   22      2.0
  2   c   356     3.0
  3   d   412     4.0
  4   f   54      5.0
  5   g   634     6.0
  6   h   72      7.0
  7   j   812     8.0
  8   k   129     9.0
  9   l   110     10.0
  10  m   200     11.0
  11  q   812     NaN
  12  z   129     NaN
  13  w   110     NaN
  </code></pre>