title: How to subtract one dataframe from another
body: <p>I have a dataframe from which I create a subset. I want to subtract that subset from the dataframe and then use the dataframe for other subsetting. How can this be done?</p>
  
  <p>Example:</p>
  
  <pre><code>     Col1 Col2 Col3 Col4
  Row1
  Row2
  Row3
  Row4
  </code></pre>
  
  <p>The subset I want is:</p>
  
  <pre><code>     Col1 Col2 Col3 Col4
  Row1
  Row2
  </code></pre>
  
  <p>and I want to be left with </p>
  
  <pre><code>     Col1 Col2 Col3 Col4
  Row3
  Row4
  </code></pre>
  
  <p>This is an example of a much bigger dataset and really I'm not looking for an answer does a subset A and then creates another subset that is not subset A. Is there a way of doing something like <code>dataframe&lt;-dataframe-subset?</code></p>