title: Filter out rows from one data.frame that are present in another data.frame
body: <p>Suppose I have a larger data.frame and a smaller one. If the smaller one is contained inside the larger one, how can I subtract the rows of the smaller data.frame, leaving a result with the difference:</p>
  
  <blockquote>
    <p>Larger - Smaller</p>
  </blockquote>
  
  <p>Example:</p>
  
  <p>Small data.frame:</p>
  
  <pre><code>     ID       CSF1PO CSF1PO.1 D10S1248 D10S1248.1 D12S391 D12S391.1
  203079_BA_M     10       11       14         16      -9        -9
  203079_BA_F      8       12       14         17      -9        -9
  203080_BA_M     10       12       13         13      -9        -9
  </code></pre>
  
  <p>Big data.frame:</p>
  
  <pre><code>      ID      CSF1PO CSF1PO.1 D10S1248 D10S1248.1 D12S391 D12S391.1
  203078_MG_M     -9       -9       15         15      18        20
  203078_MG_F     -9       -9       14         15      17        19
  203079_BA_M     10       11       14         16      -9        -9
  203079_BA_F      8       12       14         17      -9        -9
  203080_BA_M     10       12       13         13      -9        -9
  203080_BA_F     10       11       14         16      -9        -9
  203081_MG_M     10       12       14         16      -9        -9
  203081_MG_F     11       12       15         16      -9        -9
  203082_MG_M     11       11       13         15      -9        -9
  203082_MG_F     11       11       13         14      -9        -9
  </code></pre>
  
  <p>The small data.frame corresponds to the rows 3, 4 and 5 of the larger data.frame.</p>