title: equivalent of ruby Hash#reject in coffeescript
body: <p>What's the closest equivalent to ruby's Hash#reject/delete_if method?</p>
  
  <pre><code>{a:1, b:2, c:3, d:4}.reject { |k,v| v &gt; 2 }
  =&gt; {:a=&gt;1, :b=&gt;2}
  </code></pre>
  
  <p>this quick version uses <code>key, value of &lt;Object&gt;</code> but it's not elegant, and lacks the ability to pass an arbitrary condition (as a block or otherwise)</p>
  
  <pre><code>params = {a:1, b:2, c:3}
  filter = (hash)-&gt;
      result = {}
      (result[key] = value unless value &gt; 2) for key, value of params
      result
  
  console.log(filter(params))
  </code></pre>
  
  <p>underscore has a similar <code>_.omit</code> method, but only works on keys.</p>