Fastest way to delete non-contiguous lines in list field

[Richard Gaskin]

Jan Schenkel wrote:

>>>> What's the fastest way to delete non-contiguous
>>>> lines in a list field? These
>>>> lines would be listed in the "hilitedLines".
>> ... 
> *sniffles* that's the second time in as many days that
> 'repeat for each' has betrayed me. *sobs*

'repeat for each' seems to remain the saviour of each version; it's the sort
that seems to be the difference.

> By the way, the second script won't work correctly if
> the user also selected the last line of the list
> *grin*

Good catch -- fixed below (along with displaying output to avoid such
oversights going forward <g>).
 
> Out of curiosity, how fast is this 'obvious' script in
> comparison ?
> 
> repeat for each line tLine in tOrigList
> add 1 to i
> if i is not among the items of tSelLines
> then put tLine & return after tList
> end repeat
> delete char -1 of tList

It benchmarks as the slowest of the three.

Here's an interesting thing:  Test 2 is faster only when the number of
selected lines is a fraction of the total lines.  When the number of
selectedlines is greater than about 20% of the total lines, Test 1 (your
original algorithm) is faster.

Given the greater clarity of your Test 1 and more general speed, I would
advocate using that one.  Good work.

This exercise carries a side benefit: it shows that "best" is sometimes not
an absolute, depending on the usage context.

Here's all three in a single script:


on mouseUp
  put 1000 into n -- iterations
  put fld 1 into tOrigList
  put the hilitedLines of fld 1 into tSelLines
  --
  -- Test 1:  Jan, 30 June
  put the millisecs into t
  repeat n
    --
    put empty into tList1
    put tOrigList into tList1
    sort items of tSelLines numeric descending
    repeat for each item tLine in tSelLines
      delete line tLine of tList1
    end repeat
    --
  end repeat
  put the millisecs - t into t1
  --
  -- Test 2: Richard, 30 June
  put the millisecs into t
  repeat n
    --
    put empty into tList2
    put tOrigList&cr into tList2
    repeat for each item tLine in tSelLines
      put "ARBITRARY_DELETE_FLAG" into line tLine of tList2
    end repeat
    replace "ARBITRARY_DELETE_FLAG"&cr with empty in tList2
    --
  end repeat
  delete char -1 of tList2
  put the millisecs - t into t2
  --
  -- Test 3:  Jan, 1 July
  put the millisecs into t
  repeat n
    --
    put empty into tList3
    put 0 into i
    repeat for each line tLine in tOrigList
      add 1 to i
      if i is not among the items of tSelLines
      then put tLine & return after tList3
    end repeat
    delete char -1 of tList3
    --
  end repeat
  put the millisecs - t into t3
  --
  put t1 && t2  && t3 &cr&&cr& tList1 &cr&cr& tList2 &cr&cr& tList3
end mouseUp


-- 
 Richard Gaskin 
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