deleteDups()

[Mark Smith]

I'm getting the split version as about 10% faster than 'repeat for each'

Rev 2.6.1
Mac PB G4 1.5Ghz

Mark

On 16 Nov 2005, at 17:44, Alex Tweedly wrote:

> Geoff Canyon wrote:
>
>>
>> Bother -- it happened again. First we had repeat for each turning  
>> up  faster than the filter command. Now I've done a test on the   
>> following, and it looks like the split command takes not quite  
>> twice  as long as repeat for each (when repeat for each is handled  
>> the  following way).
>>
>> function deleteDupes pList -- does _not_ retain sort order
>>   repeat for each line L in pList
>>     put 1 into temp[L]
>>   end repeat
>>   return the keys of temp
>> end deleteDupes
>>
>>
> I wonder if this is because the "split" method used a secondary  
> delimiter (numtochar(3)) which doesn't exist in the data. (Nothing  
> to do with the choice of secondaryDelimiter - you need to pick one  
> that isn't in the data).
>
> So the effort involved in the "split" is
>
>   search for next linedelimiter
>   search within that line for the secondaryDelimiter
>            (which isn't there, so needs to scan all the way through  
> each line)
>   create the array element
> (i.e. every character is scanned twice).
>
> In your  "repeat for each ... " version, there is only a single  
> search (for the lineDelimiter), so you're doing basically half as  
> much searching, plus a little bit of loop overhead.
>
> That fits the data (given huge dollops of hindsight :-), though it  
> is still surprising and maybe disappointing.
>
>
> -- 
> Alex Tweedly       http://www.tweedly.net
>
>
>
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