title: Multiply values in several columns by the values in one column
body: <p>I have the following data:</p>
  
  <pre><code>ID &lt;- c("CB1", "CB2","CB3")
  size &lt;- c(10, 40, 4)
  Year.1 &lt;- c(10, 6, 15)
  Year.2 &lt;- c(12, 7, 20)
  Year.3 &lt;- c(14, 8, 25)
  data &lt;- data.frame(ID, size, Year.1, Year.2, Year.3)
  </code></pre>
  
  <p>I want to multiply the values for all years, by the values in the 'size' column (I have ten years in my actual data frame). The data should end up looking like this. </p>
  
  <pre><code>ID &lt;- c("CB1", "CB2","CB3")
  size &lt;- c(10, 40, 4)
  Year.1 &lt;- c(100, 240, 60)
  Year.2 &lt;- c(120, 280, 80)
  Year.3 &lt;- c(140, 320, 100)
  data &lt;- data.frame(ID, size, Year.1, Year.2, Year.3)
  </code></pre>
  
  <p>Ideally, the new values will replace the existing values for each year, as I don't really want to add another ten columns to my data frame. </p>