CODEWITHSUNDEEP
pythonalgorithmlistsorting
terratunaz
terratunaz

Reputation: 664

Selection Sort Algorithm Python

Working on implementing this algorithm using Python. I thought my logic was okay but apparently not as Python is complaining. The while loop is causing issues. If I remove that it works as expected but obviously doesn't sort the whole list. My thought process -> Use Linear Search to find the smallest number -> Append that new number to a list -> Remove that number from the current list -> Loop through that same list (but with smallest number removed) again -> Repeat process until we've gone through the entire list "x" number of times. "x" being equal to the length of the list. The problem I think I'm running into is that the list never gets updated every time I run through the for loop? I keep getting the error Line 21: ValueError: list.index(x): x not in list. Even though "x" is in the list. Any idea as to what I'm doing wrong?

"""
Selection sort algorithm.
"""

import random
ls = []
max_number = 10
while len(ls) < max_number:
    ls.append(random.randint(1,101))
print ls   

def selection_sort(items_to_sort):
    smallest_number = items_to_sort[0]
    current_number = 0
    sorted_items = []
    item_len = len(items_to_sort)
    while item_len > 0:
        for item in items_to_sort[:]:
            if item < smallest_number:
                smallest_number = item
        items_to_sort.pop(items_to_sort.index(smallest_number))    
        sorted_items.append(smallest_number)   
        item_len -= 1    
    return sorted_items
print selection_sort(ls)

Upvotes: 0

Views: 269

Answers (2)

ctj232
ctj232

Reputation: 390

It looks like you're not re-initializing the smallest_number variable, so after the first execution of your while loop - you look for a value smaller than the previous value which you just poped from the list.

When you don't find a value smaller than the previously smallest value which is no longer in the list, you try to pop the same smallest_number as in the previous iteration of the while loop. However, that value is no longer in the items_to_sort list which is why you get the ValueError

Try moving the line smallest_number = items_to_sort[0] to be the first line executed in every iteration of your while loop.

Upvotes: 2

fei_hsueh
fei_hsueh

Reputation: 171

After every while loop, you should assign items_to_sort[0] to smallest_number

current_number = 0
sorted_items = []
item_len = len(items_to_sort)
while item_len > 0:
    smallest_number = items_to_sort[0]
    for item in items_to_sort[:]:
        if item < smallest_number:
            smallest_number = item
    index=items_to_sort.index(smallest_number)
    items_to_sort.pop(index)
    print(items_to_sort)
    sorted_items.append(smallest_number)
    item_len -= 1
return sorted_items

Upvotes: 1

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