ActiveState Code

Recipe 391413: Pseudo-random string to float conversion

Convert strings to floats in the range [0, 1), using a hash function

Python 
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def hashed_float(s):
    """returns a float in the range [0, 1) based on a hash of the string.
    A given string will always return the same value, but different strings
    will return very different values."""
    import md5, struct
    [number] = struct.unpack("<H", md5.new(s).digest()[:2])
    return number / float(0xFFFF)

Discussion

I use this for creating sample test suites where each test takes a different time to complete, using each test's name as the parameter.

Comments

  1. 1. At 6:28 p.m. on 2 apr 2005, Josiah Carlson said:

    One could also use...

    import random
random.seed(STRING)
val = random.random()

    Or even bypass all modules entirely...

    def r(STRING):
    return (hash(STRING)+2.0**31)/2**32
  2. 2. At 5:14 p.m. on 9 may 2005, Ori Peleg (the author) said:

    True, but... random()'s or hash()'s results are not reproducible in other languages, nor necessarily in different versions of Python where implemenatations may change. MD5, or any other standard hash function, does guarantee reproducible results.

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