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Re: random number

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  Re: random number Michael Poeltl <michael.poeltl@univie.ac.at> - 2012-03-26 08:40 +0200
    Re: random number Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-03-26 07:24 +0000
      Re: random number Grzegorz Staniak <gstaniak@gmail.com> - 2012-03-26 07:50 +0000
        Re: random number Robert Kern <robert.kern@gmail.com> - 2012-03-26 10:36 +0100

#22159 — Re: random number

* Nikhil Verma <varma.nikhil22@gmail.com> [2012-03-26 08:09]:
> Hi All
> 
> How can we generate a 6 digit random number from a given number ?
what about this?

>>> given_number=123456
>>> def rand_given_number(x):
...     s = list(str(x))
...     random.shuffle(s)
...     return int(''.join(s))
... 
>>> print (rand_given_number(given_number))
653421

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#22161

On Mon, 26 Mar 2012 08:40:00 +0200, Michael Poeltl wrote:

> * Nikhil Verma <varma.nikhil22@gmail.com> [2012-03-26 08:09]:
>> Hi All
>> 
>> How can we generate a 6 digit random number from a given number ?
> what about this?
> 
>>>> given_number=123456
>>>> def rand_given_number(x):
> ...     s = list(str(x))
> ...     random.shuffle(s)
> ...     return int(''.join(s))
> ...
>>>> print (rand_given_number(given_number))
> 653421


That's not very random. In fact, it is *terrible* as a random number 
generator.

A truly random six digit number will include any number between 100000 
through 999999. There are exactly 900000 (nine hundred thousand) such 
numbers.

The way you generate the not-quite-random numbers, you miss out on almost 
all of them. E.g. you can generate 123456 but not 123455 or 123457.

In total, you generate only 6! = 6*5*4*3*2*1 = 720 numbers, no matter how 
many millions of times you call the function. Here is a demonstration:

>>> given = 123456
>>> def rand_num(x):
...     s = list(str(x))
...     random.shuffle(s)
...     return int(''.join(s))
... 
>>> import random
>>> results = set()
>>> for i in range(10**7):
...     results.add(rand_num(given))
... 
>>> len(results)
720

So slightly more than 99% of all the six digit numbers will never be 
generated using your method.



-- 
Steven

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#22162

On 26.03.2012, Steven D'Aprano <steve+comp.lang.python@pearwood.info> wroted:

>>> How can we generate a 6 digit random number from a given number ?
>> what about this?
>> 
>>>>> given_number=123456
>>>>> def rand_given_number(x):
>> ...     s = list(str(x))
>> ...     random.shuffle(s)
>> ...     return int(''.join(s))
>> ...
>>>>> print (rand_given_number(given_number))
>> 653421
>
>
> That's not very random. In fact, it is *terrible* as a random number 
> generator.

But isn't it what the OP requested, i.e. "6 digit random number 
*from a given number*"? That is, a random permutation of the set 
of its digits?

GS
-- 
Grzegorz Staniak   <gstaniak _at_ gmail [dot] com>

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#22167

On 3/26/12 8:50 AM, Grzegorz Staniak wrote:
> On 26.03.2012, Steven D'Aprano<steve+comp.lang.python@pearwood.info>  wroted:
>
>>>> How can we generate a 6 digit random number from a given number ?
>>> what about this?
>>>
>>>>>> given_number=123456
>>>>>> def rand_given_number(x):
>>> ...     s = list(str(x))
>>> ...     random.shuffle(s)
>>> ...     return int(''.join(s))
>>> ...
>>>>>> print (rand_given_number(given_number))
>>> 653421
>>
>>
>> That's not very random. In fact, it is *terrible* as a random number
>> generator.
>
> But isn't it what the OP requested, i.e. "6 digit random number
> *from a given number*"? That is, a random permutation of the set
> of its digits?

I would consider that to be a very odd interpretation of that request. But it 
*is* an extraordinarily vague request. I'm not sure if even the OP knows what he 
wants. I suspect he really wants something like a hash.

-- 
Robert Kern

"I have come to believe that the whole world is an enigma, a harmless enigma
  that is made terrible by our own mad attempt to interpret it as though it had
  an underlying truth."
   -- Umberto Eco

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