Fastest way to delete non-contiguous lines in list field

[Richard Gaskin]

Jan Schenkel wrote:

>> Hi all,
>> 
>> What's the fastest way to delete non-contiguous
>> lines in a list field? These
>> lines would be listed in the "hilitedLines".
...
> Your problem would be that you have to either keep
> track of the lines you have already deleted, or go
> from the bottom to the top to avoid this but then you
> can't use a 'repeat for each' construct, unless...
> Try the following :
> 
> put the text of fld "Foobar" into tText
> put the hilitedLines of fld "Foobar" into tLineNumbers
> sort items of tLineNumbers numeric descending
> repeat for each item tLineNumber in tLineNumbers
> delete line tLineNumber of tText
> end repeat
> set the text of field "Foobar" to tText

I think "sort" may be an expensive operation:

on mouseUp
  put 10000 into n -- iterations
  put fld 1 into tOrigList
  put the hilitedLines of fld 1 into tSelLines
  --
  -- Test 1:
  put the millisecs into t
  repeat n
    --
    put tOrigList into tList
    sort items of tSelLines numeric descending
    repeat for each item tLine in tSelLines
      delete line tLine of tList
    end repeat
    --
  end repeat
  put the millisecs - t into t1
  --
  -- Test 2:
  put the millisecs into t
  repeat n
    --
    put tOrigList into tList
    repeat for each item tLine in tSelLines
      put "ARBITRARY_DELETE_FLAG" into line tLine of tList
    end repeat
    replace "ARBITRARY_DELETE_FLAG"&cr with empty in tList
    --
  end repeat
  put the millisecs - t into t2
  --
  put t1 && t2  &&round( (t2/t1)*100) &"%"
end mouseUp

I don't know why the latter is as quick as it is, but here it seems about
40% faster than the one relying on "sort".

-- 
 Richard Gaskin 
 Fourth World Media Corporation
 Developer of WebMerge 2.2: Publish any database on any site
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