user2455280 user2455280 - 1 month ago 5
Python Question

How can I get the minimum and the maximum element of a list in python

If a have a list like:

l = [1,2,3,4,5]


and I want to have at the end

min = 1
max = 5


WITHOUT
min(l)
and
max(l)
.

Answer

The fastest approach I can think of would be to sort the original list and then pick the first and last elements. This avoids looping multiple times, but it does destroy the original structure of your list. This can be solved by simply copying the list and sorting only the copied list. I was curious if this was slower than just using max() and min() with this quick example script:

import time

l = [1,2,4,5,3]

print "Run 1"
t1 = time.time()
print "Min =", min(l)
print "Max =", max(l)
print "time =", time.time() - t1
print ""
print "l =", l
print ""


l = [1,2,4,5,3]
l1 = list(l)

print "Run 2"
t1 = time.time()
l1.sort()
print "Min =", l1[0]
print "Max =", l1[-1]
print "time =", time.time() - t1
print ""
print "l =", l
print "l1 =", l1
print ""


l = [1,2,4,5,3]

print "Run 3"
minimum = float('inf')
maximum = float('-inf')
for item in l:
    if item < minimum:
        minimum = item
    if item > maximum:
        maximum = item
print "Min =", minimum
print "Max =", maximum
print "time =", time.time() - t1
print ""
print "l =", l

Surprisingly, the second approach is faster by about 10ms on my computer. Not sure how effective this would be with very large list, but this approach is faster for at least the example list you provided.

Edit: I added @Martijn Pieters's simple loop algorithm to my timing script. (As timing would be the only important parameter worth exploring in this question.) My results are:

Run 1: 0.0199999809265s

Run 2: 0.00999999046326s

Run 3: 0.0299999713898s


Edit: Inclusion of timeit module for timing.

import timeit
from random import shuffle

l = range(10000)
shuffle(l)

def Run_1():
    #print "Min =", min(l)
    #print "Max =", max(l)
    return min(l), max(l)

def Run_2():
    l1 = list(l)
    l1.sort()
    #print "Min =", l1[0]
    #print "Max =", l1[-1]
    return l1[0], l1[-1]


def Run_3():
    minimum = float('inf')
    maximum = float('-inf')
    for item in l:
        if item < minimum:
            minimum = item
        if item > maximum:
            maximum = item
    #print "Min =", minimum
    #print "Max =", maximum
    return minimum, maximum


if __name__ == '__main__':
    num_runs = 10000
    print "Run 1"
    run1 = timeit.Timer(Run_1)
    time_run1 = run1.repeat(3, num_runs)
    print ""
    print "Run 2"
    run2 = timeit.Timer(Run_2)
    time_run2 = run2.repeat(3,num_runs)
    print ""
    print "Run 3"
    run3 = timeit.Timer(Run_3)
    time_run3 = run3.repeat(3,num_runs)
    print ""

    print "Run 1"
    for each_time in time_run1:
        print "time =", each_time
    print ""
    print "Run 2"
    for each_time in time_run2:
        print "time =", each_time
    print ""
    print "Run 3"
    for each_time in time_run3:
        print "time =", each_time
    print ""

My results are:

Run 1

time = 3.42100585452

time = 3.39309908229

time = 3.47903182233

Run 2

time = 26.5261287922

time = 26.2023346397

time = 26.7324208568

Run 3

time = 3.29800945144

time = 3.25067545773

time = 3.29783778232

sort algorithm is very slow for large arrays.

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