Timing methods to clip negative numbers. http://stackoverflow.com/questions/3391843/how-to-transform-negative-elements-to-zero-without-a-loop

clip_timing.py

import numpy as np
from timeit import timeit


def timing(neg_ratio=0.5):
    a0 = np.random.uniform(0, 1, 20000000) - neg_ratio
    globals = {
        'a0': a0,
        'np': np,
    }
    def fair(stmt):
        init = 'a = a0.copy(); '
        time = timeit(init+stmt, globals=globals, number=10)
        print("{:30} {:.3f}s".format(stmt, time))

    print("Timing for {:.2f}".format(ratio))
    fair('b = np.where(a>0, a, 0)')
    fair('b = a.clip(min=0)')
    fair('a[a<0] = 0')
    fair('a[np.where(a<0)] = 0')
    fair('b = a * (a>0)')
    fair('a *= a>0')
    print("")


if __name__ == '__main__':
    for ratio in np.linspace(0.0, 1.0, 11):
        timing(ratio)