title: Diff between dataframe values
body: <p>I have following dataframes and I want to find out which values are diffrent by <code>ID</code></p>
  <pre><code>a1 &lt;- data.frame(ID = paste0(LETTERS[1:4], 1:4), Col1=letters[1:4], Col2=letters[4:7])
  a2 &lt;- data.frame(ID = paste0(LETTERS[1:3], 1:3), Col1=c(&quot;a&quot;, &quot;c&quot;, &quot;b&quot;), Col2=c(&quot;f&quot;, &quot;e&quot;, &quot;d&quot;))
  
  
    ID Col1 Col2
  1 A1    a    d
  2 B2    b    e
  3 C3    c    f
  4 D4    d    g
  
  &gt; a2
    ID Col1 Col2
  1 A1    a    f
  2 B2    c    e
  3 C3    b    d
  </code></pre>
  <p>I would like to have a df like this:</p>
  <pre><code>  ID    Col1 Col2
  1 A1    TRUE  FALSE
  2 B2    FALSE TRUE
  3 C3    FALSE FALSE
  4 D4    FALSE FALSE
  </code></pre>
  <p>Edit:
  if a dataframe has diffrent columns in addtion, like</p>
  <pre><code>a2 &lt;- data.frame(ID = paste0(LETTERS[1:3], 1:3), Col1=c(&quot;a&quot;, &quot;c&quot;, &quot;b&quot;), Col2=c(&quot;f&quot;, &quot;e&quot;, &quot;d&quot;), Col3=c(&quot;f&quot;, &quot;e&quot;, &quot;d&quot;))
  </code></pre>
  <p>I would like to have something like:</p>
  <pre><code>ID    Col1  Col2    Col3
    &lt;chr&gt; &lt;lgl&gt; &lt;lgl&gt; &lt;lgl&gt;
  1 A1    TRUE  FALSE FALSE 
  2 B2    FALSE TRUE  FALSE 
  3 C3    FALSE FALSE FALSE 
  4 D4    NA    NA    NA   
  </code></pre>