title: Splice arrays in NumPy?
body: <p>I'd like to perform a splice of sorts in <a href="http://en.wikipedia.org/wiki/NumPy" rel="nofollow">NumPy</a>. Let's say I have two arrays, <code>a</code> and <code>b</code>:</p>
  
  <pre><code>&gt;&gt;&gt; a
  array([[ 1, 10],
         [ 2, 20],
         [ 5, 30]])
  &gt;&gt;&gt; b
  array([[ 1, 11],
         [ 3, 31],
         [ 4, 41]])
  </code></pre>
  
  <p>which I want to splice together into the following array, <code>c</code>:</p>
  
  <pre><code>&gt;&gt;&gt; c
  array([[  1.,  10.],
         [  2.,  20.],
         [  3.,  nan],
         [  4.,  nan],
         [  5.,  30.]])
  </code></pre>
  
  <p>That is, I splice the values from the first column of <code>b</code> into <code>a</code> without bothering about the second column.</p>
  
  <p>I could of course implement this myself pretty easily, but it would be nicer to have NumPy do it for me instead. Is that possible?</p>