Fastest way to sort in Python

Question

What is the fastest way to sort an array of whole integers bigger than 0 and less than 100000 in Python? But not using the built in functions like sort.

Im looking at th

Answer 1

We can use count sort using a dictionary to minimize the additional space usage, and keep the running time low as well. The count sort is much slower for small sizes of the input array because of the python vs C implementation overhead. The count sort starts to overtake the regular sort when the size of the array (COUNT) is about 1 million.

If you really want huge speedups for smaller size inputs, implement the count sort in C and call it from Python.

(Fixed a bug which Aaron (+1) helped catch ...) The python only implementation below compares the 2 approaches...

import random
import time

COUNT = 3000000

array = [random.randint(1,100000) for i in range(COUNT)]
random.shuffle(array)

array1 = array[:]

start = time.time()
array1.sort()
end = time.time()
time1 = (end-start)
print 'Time to sort = ', time1*1000, 'ms'

array2 = array[:]

start = time.time()
ardict = {}
for a in array2:
    try:
        ardict[a] += 1
    except:
        ardict[a] = 1

indx = 0
for a in sorted(ardict.keys()):
    b = ardict[a]
    array2[indx:indx+b] = [a for i in xrange(b)]
    indx += b

end = time.time()
time2 = (end-start)
print 'Time to count sort = ', time2*1000, 'ms'

print 'Ratio =', time2/time1