title: numpy.argmin for elements greater than a threshold
body: <p>I'm interested in getting the location of the minimum value in an 1-d NumPy array that meets a certain condition (in my case, a medium threshold). For example:</p>
  
  <pre><code>import numpy as np
  
  limit = 3
  a = np.array([1, 2, 4, 5, 2, 5, 3, 6, 7, 9, 10])
  </code></pre>
  
  <p>I'd like to effectively mask all numbers in <code>a</code> that are under the limit, such that the result of <code>np.argmin</code> would be 6. Is there a computationally cheap way to mask values that don't meet a condition and then apply <code>np.argmin</code>?</p>