user3671704 - 1 year ago 85
Python Question

# Random walker code python

How cold you speed up the following code to be able to do more than 100 individuals?

``````""" Random Walker """
import numpy as np
import scipy as sp
import random as rd
import time

def procedure():
time.sleep(2.5)
t0C = time.clock()
t0 = time.time()

"""Definitions"""

def ifilterfalse(predicate, iterable):
# ifilterfalse(lambda x: x%2, range(10)) --> 0 2 4 6 8
if predicate is None:
predicate = bool
for x in iterable:
if not predicate(x):
yield x

def unique_everseen(iterable, key=None):
"List unique elements, preserving order. Remember all elements ever seen."
# unique_everseen('AAAABBBCCDAABBB') --> A B C D
# unique_everseen('ABBCcAD', str.lower) --> A B C D
seen = set()
if key is None:
for element in ifilterfalse(seen.__contains__, iterable):
yield element
else:
for element in iterable:
k = key(element)
if k not in seen:
yield element

"""Creating the Random Walk"""

n=int(input('Number of Individuals at Table: '))
iters=10000
final=np.zeros(n)
total=0
for j in xrange(iters):
d=np.array([0])
i=0
while i<1:
new=d[len(d)-1]+rd.choice([-1,1])
if new<0:
new+=n
elif new>=n:
new-=n
d=np.append(d,new)
dshort=list(unique_everseen(d))
if len(dshort)>=n:
i=1
last=dshort[len(dshort)-1]
length=len(d)
final[last]+=1
total+=length

final=np.round(final/iters,4)
total=round(total/iters,3)

"""Writing To A File"""

print (40 * '-')
print (" ")
print ("   Percentages: ")
print (" ")
print ("   S#:"+"      S#:".join(map(str,range(n))))
print ("   "+"%   ".join(map(str,final))+"%")
print (" ")
print ("   Average Number of Passes of Plate: {}".format(total))
print (" ")
print (40 * '-')

# measure process time
print time.clock() - t0C, "seconds process time"

# measure wall time
print time.time() - t0, "seconds wall time"

if __name__ == "__main__":
procedure()
``````

right now for the case of 10 individuals the time is:

5.877529 seconds process time

12.9134569168 seconds wall time

The problem is that when the number of individuals(100, 1000) increases the code is too slow, any suggestions?

The problem is that `unique_everseen` is doing practically the same work in successive executions, consuming too much time. Here is a simplified version that removes `unique_everseen` function and `d` list and use a `seen` set directly in the main loop and `last` var to keep the last item:

``````""" Random Walker """
import random as rd
import time

def procedure():
n = int(input('Number of Individuals at Table: '))

t0C = time.clock()
t0 = time.time()

iters = 10000
final = [0] * n
total = 0
for j in xrange(iters):
last = 0
count = 1
seen = set([0])
while len(seen) < n:
count += 1;
new = last + rd.choice([-1, 1])
if new < 0:
new += n
elif new >= n:
new -= n
last = new
final[last] += 1
total += count

final = [round(float(f) / iters, 4) for f in final]
total = round(float(total) / iters, 3)

"""Writing To A File"""

print(40 * '-')
print(" ")
print("   Percentages: ")
print(" ")
print("   S#:" + "      S#:".join(map(str, range(n))))
print("   " + "%   ".join(map(str, final)) + "%")
print(" ")
print("   Average Number of Passes of Plate: {}".format(total))
print(" ")
print(40 * '-')

# measure process time
print time.clock() - t0C, "seconds process time"

# measure wall time
print time.time() - t0, "seconds wall time"

if __name__ == "__main__":
procedure()
``````

Note that removing the `numpy` dependency allows the script be run with `pypy`

Some results (in secods)

• for 10 individuals
• python: 0.472
• pypy: 0.084
• for 100 individuals
• python: 49.352
• pypy: 3.256
• for 500 individuals
• pypy: 80.460
• for 1000 individuals
• pypy: 318.392
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