title: In 1D array 'a' find indexes of 'a' at which 'a'='b', where 'b' are random values of 'a'
body: <p>This is my first attempt to use Python. I would appreciate any advice on how to post process data using Python.</p>
  
  <p>I have a 2D array with two columns that consists of numbers: <code>a</code> and <code>c</code>. In addition, I have 1D array <code>b</code> that consists of some specific (and exact) values of <code>a</code>. What I want to do is to find <code>c</code> values at which <code>a == b</code>. My approach is to find indexes of <code>a</code> where <code>a == b</code> and then use <code>b[a_indexes]</code>. I fail at finding indexes.</p>
  
  <pre><code>    'a'    'c'  
       1     20   
       40    70
       83    67
       1054  90
  
       'b'
        40
        1054
  </code></pre>
  
  <p>Desired output:</p>
  
  <pre><code>40 70
  1054 90
  </code></pre>
  
  <p>I tried: </p>
  
  <pre><code>a_indexes = a.index(b) 
  </code></pre>
  
  <p>But it does not work.</p>
  
  <p>I have this error: </p>
  
  <blockquote>
    <p>'numpy.ndarray' object has no attribute 'index'</p>
  </blockquote>