39 — Sorting — putting a list in order

A loaded list arrives in the order it was written, which is rarely the order you want to show. Python's sort method puts the list in order and sorted() builds a sorted copy; this guide loads numbers from JSON, sorts them both ways, and explains the difference between the two.

#Steps

1. Create numbers.json with one JSON list of numbers:

   [5, 2, 9, 1, 7, 3]
   

   copyrun it →

   Guide 30 used the same file; the numbers here are deliberately out of order.

2. Load the list with json_load from guide 14:

   use file latest
   numbers = json_load("numbers.json")
   show f"Loaded {len(numbers)} numbers: {numbers}"
   

   copyrun it →

   Run it; it prints Loaded 6 numbers: [5, 2, 9, 1, 7, 3].

3. sorted(numbers) returns a NEW list in ascending order and leaves the original untouched:

   numbers = [5, 2, 9, 1, 7, 3]
   ascending = sorted(numbers)
   show ascending
   show numbers
   

   copyrun it →

   It prints [1, 2, 3, 5, 7, 9] and then [5, 2, 9, 1, 7, 3] — the original stays exactly as it was.

4. numbers.sort() changes the list ITSELF, in place. After the call the variable holds the sorted list and the old order is gone:

   numbers = [5, 2, 9, 1, 7, 3]
   numbers.sort()
   show numbers
   

   copyrun it →

   It prints [1, 2, 3, 5, 7, 9]. This is the "ascending" order — the smallest first, the largest last.

5. Descending order flips it, the largest first. sorted(numbers, reverse=True) makes a new list without touching numbers:

   numbers = [1, 2, 3, 5, 7, 9]
   descending = sorted(numbers, reverse=True)
   show descending
   

   copyrun it →

   It prints [9, 7, 5, 3, 2, 1].

6. Now the whole report in one file. Save sorting.nme:

   # Sorting: putting a saved list of numbers in order.
   # Run: nme r sorting
   # The file numbers.json must exist in the same folder.
   
   use file latest
   
   numbers = json_load("numbers.json")
   
   show f"Loaded {len(numbers)} numbers: {numbers}"
   show ""
   
   ascending = sorted(numbers)
   show "sorted(numbers) makes a NEW list:"
   show ascending
   show "The original list is unchanged:"
   show numbers
   show ""
   
   numbers.sort()
   show "numbers.sort() changes the list IN PLACE:"
   show numbers
   show ""
   
   descending = sorted(numbers, reverse=True)
   show "Descending order with reverse=True:"
   show descending
   
   show "Smallest: " + str(numbers[0])
   show "Largest: " + str(numbers[-1])
   
   show ""
   show "Sorted list, one number per line:"
   for n in numbers:
       show "  " + str(n)
   

   copyrun it →

7. Run it with the data file present:

   nme r sorting
   

   copy

   Loaded 6 numbers: [5, 2, 9, 1, 7, 3]
   
   sorted(numbers) makes a NEW list:
   [1, 2, 3, 5, 7, 9]
   The original list is unchanged:
   [5, 2, 9, 1, 7, 3]
   
   numbers.sort() changes the list IN PLACE:
   [1, 2, 3, 5, 7, 9]
   
   Descending order with reverse=True:
   [9, 7, 5, 3, 2, 1]
   Smallest: 1
   Largest: 9
   
   Sorted list, one number per line:
     1
     2
     3
     5
     7
     9
   

   copy

   numbers.sort() changed the list for good, which is why the descending line starts from the sorted order and the one-per-line list uses it too.

8. Korean writes the same steps with 파일 사용 최신 and json읽기. The full Korean program is in the Korean guide.

#Try it yourself

Change numbers.json to [100, 3, 42, 17] and rerun sorting.nme; every order updates. Then add numbers.reverse() after the sort and rerun — the list now runs largest to smallest.

#What you learned

• sorted(numbers) returns a new ascending list and leaves the original alone.
• numbers.sort() reorders the list in place; the old order is lost.
• sorted(numbers, reverse=True) builds a descending copy.
• After sorting, numbers[0] is the smallest and numbers[-1] the largest.
• Ascending means smallest first; descending means largest first.