title: Multiply each column by their relative factor using prefix column name
body: <p>I have a matrix like</p>
  <pre><code>id |v1_m1 v2_m1 v3_m1 f_m1 v1_m2 v2_m2 v3_m2 f_m2| 
  1  |  0     .5    .5    4   0.1   0.3    0.6   4 |
  2  |  0.3   .3    .4    8   0.2   0.4    0.4   7 |
  </code></pre>
  <p>What I want is to mulply each v's in m1 by the f_m1 column, and all the v's columns with the suffix &quot;_m2&quot; by ghe f_m2 column.</p>
  <p>The output that I expect is something like this:</p>
  <pre><code>id |v1_m1 v2_m1 v3_m1 v1_m2 v2_m2 v3_m2 | 
  1  |  0    2      2    0.4   1.2   2.4  |
  2  | 2.4  2.4    3.2   1.4   2.8   2.8  |
  </code></pre>