title: Sum of columns from different data frames (different lengths) in R
body: <p>I am new to R and I have to do something as:
  I have to get a final result of the following: final_x=df1+df2+df3
  where df1, df2, and df3 are three data frames with 1 column each (but different lengths) as follows:</p>
  <p><code>df1</code></p>
  <pre><code>      x1
  1.    1
  2.    4
  3.    4
  4.    6
  </code></pre>
  <p><code>df2</code></p>
  <pre><code>      x2
  1.     1
  2.     4
  3.     4
  4.     6
  5.     6
  6.     6
  7.     8
  </code></pre>
  <p><code>df3</code></p>
  <pre><code>       x3
  1.     1
  2.     4
  3.     4
  4.     6
  5.     6
  </code></pre>
  <p>As a final result, I would like my final_x to be the following:</p>
  <p><code>final_x</code></p>
  <pre><code>      final
  1.       3
  2.      12
  3.      12
  4.      18
  5.      12
  6.      6
  7.      8
  </code></pre>
  <p>So to get the sum of each element from the columns, despite their different lengths. Basically, when I try to sum them up, I get the error saying '+' only defined for equally-sized data frames.</p>