30 — Data: statistics on a list

A saved JSON list is ready-made data for a program. This guide loads a list of numbers from a file, computes a summary by hand and with the Python standard library, and prints one report. use file reads the data; statistics does the math.

#Steps

1. Create the data file numbers.json with one JSON list:

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

   copyrun it →

   Six numbers stored as a JSON list. Guide 14 saved a dict with json_save; a JSON list is the same idea, one value per entry.

2. Load the list with use file latest and json_load. The loaded value is a Python list, so len(numbers) counts it. Save this as load.nme:

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

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   Run nme r load; it prints Loaded 6 numbers. Because the file holds a list, json_load returns a list rather than the dict from guide 14.

3. Import mean and median from the standard library. Guide 24 showed from datetime import date; importing two names at once works the same way:

   use file latest
   from statistics import mean, median
   
   numbers = json_load("numbers.json")
   show f"Mean: {mean(numbers)}"
   show f"Median: {median(numbers)}"
   

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   Run it; you see Mean: 4.5 and Median: 4.0. mean adds the values and divides by the count; median is the middle value once the list is sorted.

4. max(...) is a Python builtin, so no import is needed:

   numbers = [5, 2, 9, 1, 7, 3]
   show f"Max: {max(numbers)}"
   

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   It prints Max: 9. min(numbers) would print 1.

5. Now the whole report in one file. Save numbers.nme:

   # numbers.nme — statistics on a list of numbers saved as JSON.
   # Run: nme r numbers
   # The file numbers.json must exist in the same folder.
   
   use file latest
   from statistics import mean, median
   
   # Load the saved list of numbers.
   numbers = json_load("numbers.json")
   
   # Show what we loaded, one row per number.
   show f"Loaded {len(numbers)} numbers from numbers.json:"
   for n in numbers:
       show f"  {n}"
   
   # Count and total by hand with a for loop.
   count = 0
   total = 0
   for n in numbers:
       count = count + 1
       total = total + n
   
   # Find the biggest value by hand.
   biggest = numbers[0]
   for n in numbers:
       if n > biggest:
           biggest = n
   
   # The hand-written average...
   average = total / count
   show ""
   show f"Count: {count}"
   show f"Total: {total}"
   show f"Average by hand: {average}"
   
   # ...then the standard library does the same jobs in one call.
   show f"Mean from statistics: {mean(numbers)}"
   show f"Median from statistics: {median(numbers)}"
   
   # max() is a Python builtin, so no import is needed.
   show f"Max by hand: {biggest}"
   show f"Max from max(): {max(numbers)}"
   

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   Run it with the data file present:

   nme r numbers
   

   copy

   Loaded 6 numbers from numbers.json:
     5
     2
     9
     1
     7
     3
   
   Count: 6
   Total: 27
   Average by hand: 4.5
   Mean from statistics: 4.5
   Median from statistics: 4.0
   Max by hand: 9
   Max from max(): 9
   

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   The hand-written loop shows what mean and max do inside: a running total and a running biggest value. The statistics lines give the same answers in one call each.

6. Korean writes the same steps with 파일 사용 최신 and json읽기. The full Korean program is in the Korean guide; this snippet loads the list:

   파일 사용 최신
   숫자들 = json읽기("numbers.json")
   말해 f"숫자 {len(숫자들)}개를 불러왔습니다"
   

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#Try it yourself

Change numbers.json to [10, 20, 30] and rerun numbers.nme; the mean, the median, and the max all change together. Then add show f"Min: {min(numbers)}" to the report.

#What you learned

• json_load returns a list when the file holds a JSON list.
• from statistics import mean, median imports two standard-library names.
• mean(numbers) and median(numbers) summarize a whole list in one call.
• max(numbers) and min(numbers) are Python builtins, so no import is needed.
• A hand-written loop can find the same total and max one step at a time.