Compacting Number values into shorter string-CodePudding

I have 1296 random values ranging 0-31. I want to represent this information so let’s say I just concatenate all 1296 values into a string. If I were to do that the string would be about 2500 characters long. How can I store this information in a shorter string so I can still know all 1296 values in the correct order but not have such a long string? (I managed to get it to 648, but wanted to see if someone has an even better way)

CodePudding user response：

You can easily store 32 unique values in one character, which means your 1296 numbers can fit in a string of 1296 characters.

For example:

import random

numbers = [random.randint(0, 31) for i in range(1296)]

def numbers_to_string(numbers):
    return "".join(chr(ord("0")   number) for number in numbers)

def numbers_from_string(string):
    return [ord(char) - ord("0") for char in string]

numbers_str = numbers_to_string(numbers)
numbers_roundtrip = numbers_from_string(numbers_str)

print(numbers_roundtrip == numbers)

Output:

True

These are the numbers and the characters used to represent them:

CodePudding user response：

This will work when the range of numbers in the input list are 0-31 (inclusive) and when the list length is a multiple of 3

import random

numbers = [random.randint(0, 31) for _ in range(1296)]

def pack(n):
    result = []
    for i in range(0, len(n), 3):
        a = n[i] << 10 | n[i 1] << 5 | n[i 2]
        result.append(chr(a))
    return ''.join(result)

def unpack(s):
    result = []
    for c in s:
        o = ord(c)
        for shift in 10, 5, 0:
            result.append(o >> shift & 0x1F)
    return result

packed = pack(numbers)
print(len(packed))
result = unpack(packed)
assert result == numbers

Output:

Note:

If the range of numbers was 1-31 then this technique (with a minor modification) could be used for any list length because zero could be used as a padding indicator