title: What is the most efficient way to check if a value exists in a NumPy array?
body: <p>I have a very large NumPy array</p>
  
  <pre><code>1 40 3
  4 50 4
  5 60 7
  5 49 6
  6 70 8
  8 80 9
  8 72 1
  9 90 7
  .... 
  </code></pre>
  
  <p>I want to check to see if a value exists in the 1st column of the array.  I've got a bunch of homegrown ways (e.g. iterating through each row and checking), but given the size of the array I'd like to find the most efficient method.</p>
  
  <p>Thanks!</p>