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Re: [xsl] How to Do Random "Shuffle"?


Subject: Re: [xsl] How to Do Random "Shuffle"?
From: "David Rudel fwqhgads@xxxxxxxxx" <xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx>
Date: Thu, 18 Sep 2014 11:34:30 -0000

That is not what random:random-sequence does. It creates a sequence of
N random numbers between 0 and 1.

But if you then find the index of each of these numbers in the sorted
version of this sequence, **then** you have created a random
permutation of the numbers from 1 to N, as the OP requested.

So, by way of example, let's say random:random-sequence(5) spits out
(0.413,0.192,0.888,0.513,0.522)

Then the sorted version is (0.192,0.413,0.513,0.522,0.888).

Taking each element (in sequence) from the original output of
random:random-sequence() and finding the index in the sorted sequence
yields (2,1,5,3,4), a random permutation of the numbers from 1 to 5.


On Thu, Sep 18, 2014 at 1:14 PM, Wolfgang Laun wolfgang.laun@xxxxxxxxx
<xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx> wrote:
> random:random-sequence(N)
>
> If this is supposed to produce a sequence of numbers in the range 1..N
while
> expecting it to contain every number of that range exactly once: would this
> truly be a "random" sequence? I don't think so.
>
> -W
>
>
>
> On 18 September 2014 11:05, David Rudel fwqhgads@xxxxxxxxx
> <xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx> wrote:
>>
>> When I have to do this (essentially create a permutation of the numbers
>> from 1 to N), I combine random:random-sequence with saxon:sort
>>
>> I'm away right now so I'm not working on a machine with XSLT, so the
>> following syntax may be off, but I use:
>>
>> <xsl:variable name="rand" select="random:random-sequence(N)"/>
>>
>> <xsl:variable name="sorted.rand" select="saxon:sort($rand)"/>
>>
>> <xsl:variable name="permutation" select="$rand!index-of($sorted.rand,.)"/>
>>
>> The select attribute of the last can also be written as "for $i in $rand
>> return index-of($sorted.rand,$i)"  .
>>
>>
>> On Saturday, September 13, 2014, Eliot Kimber ekimber@xxxxxxxxxxxx
>> <xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx> wrote:
>>>
>>> Using XSLT 2 I need to implement rendering of "match table" questions
>>> where you have two sets of items, the match item and the thing it matches
>>> to. I want to present this as a literal table, where the first column is
>>> the match-from items in source order and the second column is the
>>> match-to
>>> items, in random order.
>>>
>>> I think this is best characterized as a "shuffle" problem, where you want
>>> to reorder a list randomly but all items in the list must be accounted
>>> for.
>>>
>>> I can think of a recursive algorithm: given a list, generate a random
>>> integer between 1 and the list length, select that item and add it to the
>>> result list, then call this function on the original list minus the node
>>> you just selected.
>>>
>>> Is there an easier or more efficient way to do it?
>>>
>>> Thanks,
>>>
>>> Eliot
>>> bbbbb
>>> Eliot Kimber, Owner
>>> Contrext, LLC
>>> http://contrext.com
>>>
>>>
>>
>>
>> --
>>
>> "A false conclusion, once arrived at and widely accepted is not dislodged
>> easily, and the less it is understood, the more tenaciously it is held." -
>> Cantor's Law of Preservation of Ignorance.
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--

"A false conclusion, once arrived at and widely accepted is not
dislodged easily, and the less it is understood, the more tenaciously
it is held." - Cantor's Law of Preservation of Ignorance.


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