title: filter the item whose first element is more than twice repeated in array
body: <p>I have an array and want to filter the item whose first element is more than twice repeated in this array.</p>
  <p>Friends, how can I do this?.</p>
  <pre><code> arr=[
  [a,1],
  [a,2],
  [a,4],
  [b,2],
  [C,2],
  [d,2],
  [e,2],
  [e,2],
  [n,2],
  ...
  ]
  </code></pre>
  <p>I want the result of the filter to be like below</p>
  <pre><code> result=[
  [a,1],
  [a,2],
  [a,4],
  [e,2],
  [e,2],
  ...
  ]
  </code></pre>