Deleting Data Woefully Slow

[Alex Tweedly]

Kay C Lan wrote:
> On Thu, Mar 25, 2010 at 8:08 PM, Richard Gaskin
> <ambassador at fourthworld.com>wrote:
>
>   
>> Moreover, Raney once noted that he took the time to optimize
>> "put...after..." specifically for cases like yours, so it could be used in
>> conjunction with "repeat for each" to build a subset of data.
>>
>> Richard,
>>     
>
> any thoughts as to why delete line -1 is so so much slower than delete line
> 1? Seems illogical.
>   
delete line 1    requires
    search for 1st CR (i.e. scan 30-80 chars)
     either :       copy from there to the end (i.e. move each character).
           or:       manipulate some pointer to say where the data starts
I don't know which of these rev does.


delete line -1   requires
     search for every CR   (i.e. scan every char in the whole large 
piece of data)
      adjust some pointer to truncate

Scanning is much slower than simply copying.

You can see this by comparing the times for
>   put the milliseconds into tStart
>    repeat K timeScale
>       put the number of lines in largeData into t
>    end repeat
>    put the milliseconds - tStart & CR after field "F"
>    
>    put the milliseconds into tStart
>    repeat K times
>       put largedata into t
>    end repeat
>    put the milliseconds - tStart & CR after field "F"
>   
-- Alex.