title: Removing rows when reading data D3
body: <p>Say I have a sample file sample.csv:</p>
  
  <pre><code>row,col,value
  1,1,2
  1,2,3
  1,3,NA
  </code></pre>
  
  <p>When reading data in d3 you do something like:</p>
  
  <pre><code>d3.csv("sample.csv", function(data) {
      data.forEach(function(d) {
      d.value = +d.value;
  });
  </code></pre>
  
  <p>However, for the NA value +d.value will return NaN. How can I exclude NaN values from my data. i.e. read the data, and only take rows which have a number value</p>
  
  <p>Thanks!</p>