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Selection Sort Algorithm Explained (Full Code Included) - Python Algorithms Series for Beginners

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Continuing the Python algorithm series with Selection Sort. Check out the full playlist here:
• Bubble Sort Algorithm ...
The Selection Sort Algorithm starts by setting the first item in an unsorted list as the position with the lowest (minimum) value. We then use this to compare each of the items to the right. Whenever we find a new item with a lower value, that becomes our new minimum value and we continue on.
After one iteration of the selection sort algorithm, we create two sublists. One will be for unsorted items and the other will be for sorted ones. We move the minimum item from the unsorted sublist into the last position of our sorted sublist.
After we finish all the iterations, we should be left with only the largest number in our unsorted sublist (which is now sorted to the highest position as it is the highest value.)
The selection sort algorithm has a complexity of O(n^2) still but nearly always outperforms the bubble sort algorithm in situations where writing is important (fewer switches, more efficient per iteration).
If you had any questions about the selection sort algorithm, or any of the other algorithms in this series - please let me know in the comments below!
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#Python #Algorithm #SelectionSort
*****************************************************************
Full code from the video:
def selection_sort(list_a):
indexing_length = range(0, len(list_a)-1)
for i in indexing_length:
min_value = i
for j in range(i+1, len(list_a)):
if list_a[j] #less than list_a[min_value]: #"angled brackets not allowed in youtube description"
min_value = j
if min_value != i:
list_a[min_value], list_a[i] = list_a[i], list_a[min_value]
return list_a
print(selection_sort([7,8,9,8,7,6,5,6,7,8,9,0]))
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Packages (& Versions) used in this video:
Python 3.7
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Опубликовано:

14 авг 2024

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Комментарии : 93

@janmuhammad7376 3 года назад

I wish I have teachers like him at my college

@utkarshmalik4471 3 года назад

Hey Derrick this is the best Algorithm Playlist I ever came across So please it's a humble request to make more videos on Algorithm

@thatcherkane4955 3 года назад

Sorry to be off topic but does anybody know a way to log back into an Instagram account?? I was stupid forgot the password. I love any assistance you can give me

@kasontrevor966 3 года назад

@Thatcher Kane instablaster =)

@thatcherkane4955 3 года назад

@Kason Trevor thanks so much for your reply. I found the site through google and Im waiting for the hacking stuff now. Looks like it's gonna take quite some time so I will reply here later when my account password hopefully is recovered.

@thatcherkane4955 3 года назад

@Kason Trevor it did the trick and I now got access to my account again. I'm so happy! Thank you so much you saved my account !

@kasontrevor966 3 года назад

@Thatcher Kane Glad I could help :)

@lovesignal 9 месяцев назад

Yeah, you're really talented at teaching. Believe me when I say you've got a real gift. And thank you for sharing it because you don't know how daunting this concept was to me when hearing it from other instructors.

@navodyaliyanage473 3 года назад

this is absolutely the best series on algorithms, I struggled a lot watching other videos, but this is really amazing, clear and short.

@andrewbrower4158 3 года назад

This tutorial is incredible. Thank you for teaching it so effectively

@AlfredDHull 3 года назад

Still loving this video two years later Derrick!

@johnhillescobar 5 лет назад

This is a great, amazing and super instructional video. My code for this algorithm is by far more complex. Love the code you created.

@aqualung1466 2 года назад

@Maryam Ashraf Below is what I did to test - setup params for "my_range" and "num_elements", or do like I did and make these arguments to your script with sys.argv. import sys import time import random my_range = int(sys.argv[1]) num_elements = int(sys.argv[2]) my_array = [random.randint(1, my_range) for i in range(0, num_elements)] start_time = time.time() bubble_sorted_array = list(bubble_sort(my_array)) bubble_sort_run_time = time.time() - start_time start_time = time.time() selection_sorted_array = list(selection_sort(my_array)) selection_sort_run_time = time.time() - start_time selection_sort_efficiency = bubble_sort_run_time / selection_sort_run_time print("bubble sort took {:.2f} seconds to run".format(bubble_sort_run_time)) print("selection sort took {:.2f} seconds to run".format(selection_sort_run_time)) print("selection sort was {:.2f} times more efficient than bubble sort".format(selection_sort_efficiency)) HTH

@RadioKilledMusic 4 года назад

def selection_sort(list_a): indexing_length=range(len(list_a)-1) for i in indexing_length: min_value=i for j in range(i+1,len(list_a)): if list_a[j]

@abletmuhtar8979 5 лет назад

Pls teach all of those fundamental algorithms. Thanks

@tuborao 4 года назад

Hi Derrick, first of all I would like to thank you for your videos. They are helping me a lot! I think I found an indentation error inside your script in your githup area. The "if min_value !=1" is not indented with the "for j", and this can cause some sort errors if the first element of the list is equal to the last element. thanks! for j in range(i+1, len(list_a)): if list_a[j] < list_a[min_value]: min_value = j if min_value != i: list_a[min_value], list_a[i] = list_a[i], list_a[min_value] return list_a print(selection_sort([6,7,8,7,6,5,4,5,6,7,6,7,8,9,7,9,0]))

@cassidybrookland2174 2 года назад

this fixed my error!

@coolios685 3 года назад

Dude!!! Derrick this is so awesome. you make these concepts so easy to learn. Keep it up!!!

@easynow6599 2 года назад

i have to admit.. I love your short but badass bass music at the intro..

@shrutikanikhar7987 4 года назад

You're an amazing teacher.......your videos are very helpful.... Thanks

@timohelasvuo9650 5 лет назад

Here again for another alogorithm treat! Thanks buddy for yet again great video. Looking forward to look into the code on my comp later today

@jiahuizhu3911 3 года назад

A basic question. How come the 'changing position' could work? such as list[j], list[i] = list[i], list[j]. The first assignment should change list[j], the the second assignment will come back to i, isn't it? Has python put some secrete third item to keep the value temporarily? I am a learner on Python:) Thank you very much in advance

@rahulnegi456 3 года назад

its swapping the expression: “ a, b = b, a”, first right gets assigned to first left and second right get assigned to second left at the same time therefore swap values of a and b Search for one liner swapping in python you will get it!

@aqualung1466 2 года назад

Your videos as terrific, thank you. Below is what I came up with - it is almost twice as fast as your code. Why is that?? def selection_sort(unsorted_list): sorted_list = [] while len(unsorted_list) > 0: min_index, min = 0, unsorted_list[0] for i in range(0, (len(unsorted_list) - 1)): if unsorted_list[i] < min: min_index, min = i, unsorted_list[i] sorted_list.append(unsorted_list.pop(min_index)) return sorted_list

@rayanrahmoune1064 4 года назад

I did it another way i don't know if it's selection sort def selectionsort(mylist): indexing_length = len(mylist) sorted = [] if indexing_length mylist[value]: min = mylist[value] mylist[0], mylist[value] = mylist[value] , mylist[0] mylist.pop(0) notsorted = mylist sorted.append(min) return sorted + selectionsort(notsorted)

@SEE.ME.N0.M0RE 3 года назад

Thank you so much!

@DeepakSah3.0 4 месяца назад

Love from India - Thanks

@lone.wo1f 4 года назад

Great tutorial! Easy to grasp the concepts.. Subbed!

@anirbanc88 2 года назад

you are the coolest guy ever man, thanks so much

@AlternateMelatonin Год назад

I always wonder, why my professor spends 50 mins lecture just to teach what you show in 5 mins. Thank you always.

@carloschaccon8465 5 лет назад

Awesome Derrick, Have you considered a video for Regular Expressions to find data over large files, It is just an idea, thanks again, and keep sharing your knowledge .

@user-uw3hu2bb4s 3 года назад

hey buddy thanks for helping us and i coded my own version def selectionSort(l): indexLength = range(0,len(l) - 1) for i in indexLength: minvalue = i for j in range(i+1,len(l)): if l[j] < l[minvalue]: l[j],l[minvalue] = l[minvalue],l[j] j = j -1 return l print(selectionSort([1,3,0])) this works for me!

@rushas 4 года назад

I like the new intro and the outro! Content is also great!

@mahadkhurram2950 3 года назад

Thanks bro, I have an exam tomorrow. And this is really gonna help.

@nowyouknow2249 5 лет назад

Nice video like it's really cool. Fire on bruv!

@mehmetozel9001 3 года назад

Really really easy explained I love u

@Futball860 2 года назад

Would the result be different if we used indexing_length = range(0, len(list_a))?

@xynerd 2 года назад

awesome explanation!

@alexeyigonen3170 4 года назад

Thanks for your videos. Will this code be shorter? (prints really help to see the work of the two cycles) for k in range(0,n-1): print('for cycle, k: ', k) for x in range(1, n): print("for cycle, x:",x,a) if a[k] > a[x] and x > k: a[k], a[x] = a[x], a[k]

@codex8332 4 года назад

Please I don't understand the logic behind.the last part. If the min_value != i . Please I need an explanation

@KeepCoding69 Год назад

It's not required actually u can just simply write the switch statement and it would still work.

@DispelTV 2 года назад

When I measure the time it takes to sort with bubble vs selection, selection always takes longer to execute. How is selection better than bubble if bubble takes less time and there's 2 for loops in selection sort which leads to higher complexity O(n^2)? Otherwise, fantastic and simple videos to learn from.

@dewman7477 3 года назад

I don’t get why indexing length only goes to second last item in unsourced list. What if the item in the unworried list is smaller than the previous minimum value?

@navodyaliyanage473 3 года назад

please make more videos on python..on what's after algorithms

@lyricsdelivered 2 года назад

How do you calculate time complexity

@sebastianlupa7355 3 года назад

I think calling min_value index_of_min_value could make it clearer, took me a while to figure it out :-)

@aqualung1466 2 года назад

Agreed.

@breakoutgaffe4027 2 года назад

great explanation

@abdullahshahid6216 3 года назад

Line 7: Should the min_value be equal to list_a[ i ]??? Please answer

@dhaval1489 5 лет назад

Hey Dirreck, can you please do the same in OOP, most tutorial don't cover OOP request you to do that for future videos

@hardiktmustudent5851 3 года назад

hey can you plz tell me a program for to rotate a matrix 90 degree anti-clockwise

@handle-2 3 года назад

can someone explain what this line does? its line 14 in his code list_a[min_value],list_a[i]=list_a[i],list_a[min_value]

@rahulnegi456 3 года назад

@erikcarcelen1663 4 года назад

Hey, amazing video and so beautiful explanation, but I have a question hehe How do you do your animations?

@betobernal486 4 года назад

Hi Derrick thanks for your videos. I solved in a recursive way, take a look! def selection_sort(lista,sortedd): if len(lista) !=0: mini=lista[0] for i in lista[1:]: mini=min(mini,i) sortedd.append(mini) lista.remove(mini) selection_sort(lista,sortedd) return sortedd def sorting(lista): return selection_sort(lista,[]) a=[3,3,54,2345,542,456,0,3,4,4,3,6] sorting(a) The problem is that my function requires 2 args, thats why I had to implement the second function. Is there a way to do it this way with only one function? Thanks!

@jaket750 Год назад

thanks man you saved me

@alighaith9717 5 лет назад

thank you for effort Derrick , can you help me with this issue (I have a file of 1000 images and i want to classify it at specific folders i already created for example : from pic 1 to 10 move to folder number 1 and from 12 to 15 to folder number 2 etc ....)I'm biggner on python if you help me I really appreciated it .