title: Values being altered in numpy array
body: <p>So I have a 2D numpy array (256,256), containing values between 0 and 10, which is essentially an image. I need to remove the 0 values and set them to NaN so that I can plot the array using a specific library (APLpy). However whenever I try and change all of the 0 values, some of the other values get altered, in some cases to 100 times their original value (no idea why).</p>
  
  <p>The code I'm using is: </p>
  
  <pre><code>for index, value in np.ndenumerate(tex_data):
      if value == 0:
          tex_data[index] = 'NaN'
  </code></pre>
  
  <p>where tex_data is the data array from which I need to remove the zeros. Unfortunately I can't just use a mask for the values I don't need, as APLpy wont except masked arrays as far as I can tell.</p>
  
  <p>Is there anyway I can set the 0 values to NaN without changing the other values in the array?</p>