title: Reading very large file numpy and retrieving only specific values
body: <p>I have a really large file, over one million lines. It contains two columns, both integers. The second column isn't important so I can ignore it. What I want to do is to read the file and only retrieve all the values from the first column that are less than 20,000. However, I am having issues.</p>
  <p>What I have thus far is but since the file is so large this will cause issues:</p>
  <pre><code>data = np.loadtxt(&quot;./muon.txt&quot;, usecols = (0))
  for values in data:
     if values &lt; 20,000:
       \\ store values to some array
  </code></pre>