title: How do I delete nan-valued keys from one dictionary into another dictionary
body: <p><strong>I have this dictionary :</strong></p>
  <pre><code>d = {4: {0: [12], 1: [194]}, 8: {0: [222], 1: nan}, 18: {0: [60], 1: nan},
        19: {0: [128], 1: nan}, 21: {0: [54], 1: nan}}
  </code></pre>
  <p><strong>the output should look like this:</strong></p>
  <pre><code>  d = {4: {0: [12], 1: [194]}, 8: {0: [222] }, 
         18: {0: [60] }, 19: {0: [128]}, 21: {0: [54]}}
  </code></pre>