[Gllug] [OT] sort algorithms

[Andrew Farnsworth]

David has a good point, I don't think my code will work if there are
duplicate values in your predefined list.

Andy

On Tue, Nov 29, 2011 at 5:13 PM, Andrew Farnsworth <farnsaw at stonedoor.com>wrote:

> Presuming your predefined sequence is fixed or known prior to the sort
> process, you can assign sequencial values to a hash when the keys are
> the predefined values in the predefined order.  Then sort using a custom
> sort on the values of the hash rather than the keys.  For example, in Perl,
> you could do it this way.
>
> my @predefinedList = (1,5,8,4,3,6,9);
> my %orderedHash;
> my $order = 1;
>
> foreach my $key (@predefinedList)
> {
>     $orderedHash{$key} = $order++;
> }
>
> my @unsortedList = (9,3,4,8,1);
>
> my @sortedList = sort {$orderedHash{$a} <=>
> $orderedHash{$b}} @unsortedList;
>
> print "@sortedList\n";
>
> exit;
>
> Andy F
>
>
> On Tue, Nov 29, 2011 at 4:34 PM, James Courtier-Dutton <
> james.dutton at gmail.com> wrote:
>
>> Hi,
>>
>> I have a problem with a special sort I need to do.
>> I have some ideas for an efficient solution, but I wished to ask if
>> anyone else had a better idea.
>> My current best solution is to do a transform on the source data using
>> hash lookups on the predefined sequence.
>> So the source data is changed into numbers that when sorted are in
>> numerical order, do a normal numerical sort, and then repeat the
>> inverse of the transform at the end.
>>
>> Problem is as follows.
>> Target pattern is a list of numbers in a certain predefined sequence.
>> The source data is a set of numbers that is always a subset of the
>> predefined sequence.
>> I need a way to sort the source data so that the numbers appear in the
>> same order as the predefined sequence.
>>
>> Eg.
>> Predefined sequence
>> 1  5   8  4  3   6   9
>>
>> Source data
>> 9 3 4 8 1
>>
>> Result
>> 1 8 4 3 9
>>
>> Kind Regards
>>
>> James
>> --
>> Gllug mailing list  -  Gllug at gllug.org.uk
>> http://lists.gllug.org.uk/mailman/listinfo/gllug
>>
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.lug.org.uk/pipermail/gllug/attachments/20111129/4bbc3916/attachment.html>
-------------- next part --------------
--
Gllug mailing list  -  Gllug at gllug.org.uk
http://lists.gllug.org.uk/mailman/listinfo/gllug