title: Weighted Mean as a Column in Pandas
body: <p>I am trying to add a column with the weighted average of 4 columns with 4 columns of weights</p>
  <pre><code>df = pd.DataFrame.from_dict(dict([('A', [2000, 1000, 2509, 2145]),
                                    ('A_Weight', [37, 47, 33, 16]),
                                    ('B', [2100, 1500, 2000, 1600]),
                                    ('B_weights', [17, 21, 6, 2]),
                                    ('C', [2500, 1400, 0, 2300]),
                                    ('C_weights', [5, 35, 0, 40]),
                                    ('D', [0, 1600, 2100, 2000]),
                                    ('D_weights', [0, 32, 10, 5])]))
  </code></pre>
  <p>I want the weighted average to be in a new column named &quot;WA&quot; but every time I try it displays NaN</p>
  <p>Desired Dataframe would be a new column with the following values as ex:</p>
  <p>Formula I used <code>(((A * A_weight)+(B * b_weight)+(C * C_weight)+(D * D_weight)) / sum(all weights)</code></p>
  <pre><code>df['WA'] = [2071.19,1323.70, 2363.20,2214.60 ]
  </code></pre>
  <p>Thank you</p>