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Alan G. On 24/05/2019 10:20, David Lifschitz wrote: > Hi. > I'm learning the processes of python so I'm trying to figure out how > to sort it manually. > > On Fri, May 24, 2019 at 3:00 AM Alan Gauld via Tutor <tutor@python.org > <mailto:tutor@python.org>> wrote: > > On 23/05/2019 13:16, David Lifschitz wrote: > > > The next job of the code is to sort the list of numbers that > were inputted > > in an ascending fashion. > > You are aware that Python lists have a built in sort method? > It will be more efficient than anything you can create > yourself in Python. Assuming you know that and decided > to write a sort routine for fun.... > > > > There is no error from the code, however, when I run the code > the first > > inputted number stays in its place and doesn't get sorted with > the rest of > > the numbers. > > Any advice??? > > Yes, see below: > > > emptyList = [] > > This is a terrible name since it becomes misleading the > instant you put anything into it! > > number_list or similar would be more accurate. > Or even just 'data'.... > > > nOFN = int(input("how many numbers do you want to sort: ")) > > > > for x in range(nOFN): > >?? ?? ??number1 = int(input("input number: ")) > >?? ?? ??emptyList.append(number1) > > You could have used a list comprehension: > > emptyList = [int(input("input number: ")) for n in range(nOFN)] > > Now onto the problem sort code > > > firstElement = emptyList[0] > > Why did you do this? You never refer to firstElement again... > > > n = len(emptyList) > > for j in range(1, n): > >?? ?? ??if emptyList[j-1] > emptyList[j]: > >?? ?? ?? ?? ??(emptyList[j-1], emptyList[j]) = (emptyList[j], > emptyList[j-1]) > > Consider the first case, j=1 > > If the first element is greater than the second > you swap them. Otherwise you leave them in place. > > The loop now considers elements 2 and 3. > If 2 >3 you reverse them, otherwise move on. > But if element 3 is less than element 1 you never > go back to move it to the top. > > Consider this example - [3,2,1] > > 1st iteration?? ??-> 2,3,1 > 2nd iteration?? ??-> 2,1,3 > > Loop ends. > But you never swapped 1 and 2 after(or during) the last iteration. > > Your sort routine is fundamentally flawed. You need a rethink. > But not too much because the built in sort will nearly always be > preferred! > > Incidentally, creating working sort algorithms is one of the > hardest things to get right in computing. It is one of > those things that can seem right then one specific pattern > will break it. > > -- > Alan G > Author of the Learn to Program web site > http://www.alan-g.me.uk/ > http://www.amazon.com/author/alan_gauld > Follow my photo-blog on Flickr at: > http://www.flickr.com/photos/alangauldphotos > > > _______________________________________________ > Tutor maillist?? -?? Tutor@python.org <mailto:Tutor@python.org> > To unsubscribe or change subscription options: > https://mail.python.org/mailman/listinfo/tutor > > -- > Sent from an email account -- Alan G Author of the Learn to Program web site http://www.alan-g.me.uk/ http://www.amazon.com/author/alan_gauld Follow my photo-blog on Flickr at: http://www.flickr.com/photos/alangauldphotos _______________________________________________ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
