title: Group by, take count and filter out entries corresponding to count greater than 1
body: <p>The following is my data,</p>
  
  <pre><code>data
  
  date             number     value
  2016-05-05         1          5
  2016-05-05         1          6
  2016-05-06         2          7
  2016-05-06         2          8
  2016-05-07         3          9 
  2016-05-08         4          10
  2016-05-09         5          11
  </code></pre>
  
  <p>When I use the following command,</p>
  
  <pre><code>data %&gt;% groupby(date, number) %&gt;% summarize(count = n())
  </code></pre>
  
  <p>I get the following,</p>
  
  <pre><code>date             number        count 
  2016-05-05         1             2
  2016-05-06         2             2
  2016-05-07         3             1
  2016-05-08         4             1
  2016-05-09         5             1
  </code></pre>
  
  <p>Now I want to filter out the entries corresponding to the counts greater than 1. I want to remove the combination entries which has count greater than 1. My output should be like the following,</p>
  
  <pre><code>data
  
  date             number     value
  2016-05-07         3          9 
  2016-05-08         4          10
  2016-05-09         5          11
  </code></pre>
  
  <p>where the first four entries, since it has count greater than 1 , has been filtered out. Can anybody help me in doing this? Or give some idea related to it?</p>