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POhow to speed up enumerate for numpy array / how to enumerate over numpy array efficiently?
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copied!<p>I need to generate a lot of random numbers. I've tried using <code>random.random</code> but this function is quite slow. Therefore I switched to <code>numpy.random.random</code> which is way faster! So far so good. The generated random numbers are actually used to calculate some thing (based on the number). I therefore <code>enumerate</code> over each number and replace the value. This seems to kill all my previously gained speedup. Here are the stats generated with <code>timeit()</code>:</p> <pre><code>test_random - no enumerate 0.133111953735 test_np_random - no enumerate 0.0177130699158 test_random - enumerate 0.269361019135 test_np_random - enumerate 1.22525310516 </code></pre> <p>as you can see, generating the number is almost 10 times faster using numpy, but enumerating over those numbers gives me equal run times.</p> <p>Below is the code that I'm using:</p> <pre><code>import numpy as np import timeit import random NBR_TIMES = 10 NBR_ELEMENTS = 100000 def test_random(do_enumerate=False): y = [random.random() for i in range(NBR_ELEMENTS)] if do_enumerate: for index, item in enumerate(y): # overwrite the y value, in reality this will be some function of 'item' y[index] = 1 + item def test_np_random(do_enumerate=False): y = np.random.random(NBR_ELEMENTS) if do_enumerate: for index, item in enumerate(y): # overwrite the y value, in reality this will be some function of 'item' y[index] = 1 + item if __name__ == '__main__': from timeit import Timer t = Timer("test_random()", "from __main__ import test_random") print "test_random - no enumerate" print t.timeit(NBR_TIMES) t = Timer("test_np_random()", "from __main__ import test_np_random") print "test_np_random - no enumerate" print t.timeit(NBR_TIMES) t = Timer("test_random(True)", "from __main__ import test_random") print "test_random - enumerate" print t.timeit(NBR_TIMES) t = Timer("test_np_random(True)", "from __main__ import test_np_random") print "test_np_random - enumerate" print t.timeit(NBR_TIMES) </code></pre> <p>What's the best way to speed this up and why does <code>enumerate</code> slow things down so dramatically?</p> <p><strong>EDIT:</strong> the reason I use <code>enumerate</code> is because I need both the index and the value of the current element.</p>

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