title: combine two data frames or tibbles
body: <p>I have the following data frames:</p>
  
  <pre><code>a &lt;- data.frame(Test=1:4,
              TestA=5:6)
  &gt; a
      Test TestA
  1    1     5
  2    2     6
  3    3     5
  4    4     6
  
  
  b &lt;- data.frame(TEST=1:10,
              TestB=11:20)
  
  &gt; b
      TEST TestB
  1     1    11
  2     2    12
  3     3    13
  4     4    14
  5     5    15
  6     6    16
  7     7    17
  8     8    18
  9     9    19
  10   10    20
  </code></pre>
  
  <p>And I want to combine them such that the result looks like:</p>
  
  <pre><code>    Test TestA TEST   TestB
  1     1     5    1      11
  2     2     6    2      12
  3     3     5    3      13
  4     4     6    4      14
  5     0     0    5      15
  6     0     0    6      16
  7     0     0    7      17
  8     0     0    8      18
  9     0     0    9      19
  10    0     0   10      20
  </code></pre>
  
  <p>That is, to combine with unmatched rows filled with zeros.</p>
  
  <p>I am convinced that a simple solution exists and it would be fine if there is a way with <code>dplyr</code>.</p>