42 — Compare: two groups of numbers

Guide 30 summarized one list of numbers. Comparing two lists asks the same questions twice, then decides which group is bigger.

#Steps

1. Create and load the two data files, each holding one JSON list (the shape guide 14 saved with json_save):

   # a.json
   [5, 2, 9, 1, 7, 3]
   # b.json
   [8, 4, 6, 10, 3]
   

   copyrun it →

   use file latest
   a = json_load("a.json")
   b = json_load("b.json")
   show f"a.json: {a}"
   show f"b.json: {b}"
   

   copyrun it →

   It prints a.json: [5, 2, 9, 1, 7, 3] and b.json: [8, 4, 6, 10, 3].

2. Mean by hand, mean by library, and max. sum(a) / len(a) is the mean; statistics.mean (guide 30) checks it; max is a builtin:

   from statistics import mean
   a = [5, 2, 9, 1, 7, 3]
   a_mean = sum(a) / len(a)
   show f"a mean: {a_mean}"
   show f"a mean from statistics: {mean(a)}"
   show f"a max: {max(a)}"
   

   copyrun it →

   a is 4.5 (27 over 6), with max 9. For b the sum is 31 over 5, so its mean is 6.2 and its max is 10.

3. The comparison program. Save compare.nme with both JSON files, and run it:

   # compare.nme — which group of numbers is bigger?
   # Run: nme r compare
   # The files a.json and b.json must exist in the same folder.
   
   use file latest
   from statistics import mean
   
   a = json_load("a.json")
   b = json_load("b.json")
   
   # Mean by hand, max by builtin.
   a_mean = sum(a) / len(a)
   b_mean = sum(b) / len(b)
   a_max = max(a)
   b_max = max(b)
   show f"a: mean {a_mean}, max {a_max}"
   show f"b: mean {b_mean}, max {b_max}"
   
   # statistics.mean checks the hand-written answer.
   show f"a mean from statistics: {mean(a)}"
   show f"b mean from statistics: {mean(b)}"
   
   # Compare the two groups.
   if a_mean > b_mean:
       show "a has the higher mean"
   else:
       show "b has the higher mean"
   if a_max > b_max:
       show "a has the higher max"
   else:
       show "b has the higher max"
   

   copyrun it →

   nme r compare
   

   copy

   a: mean 4.5, max 9
   b: mean 6.2, max 10
   a mean from statistics: 4.5
   b mean from statistics: 6.2
   a has the higher mean
   b has the higher max
   

   copy

   b wins both comparisons. The statistics lines confirm the hand-written means. The Korean guide uses json읽기 and 보여줘 — full pair in 42-compare.ko.md.

#Try it yourself

Change b.json to [3, 1, 4, 1, 5, 9] and rerun — the answers flip.

#What you learned

• json_load turns each JSON list file into a Python list.
• sum(numbers) / len(numbers) is the mean written by hand.
• statistics.mean gives the same answer in one call.
• max(numbers) is a builtin; if/else turns the numbers into a sentence.