Indeed. Jerry was (as usual) correct - if the engine can do it, then the
engine will normally be faster.
BUT sorting a list requires moving the data around quite a lot, AND
sorting something that actually reverses it can be a pathologically bad
case (e.g. if the engine uses any variant of quicksort())..
SO - take the original idea, and examine how it *might* be improved .....
The problem here is that "put ... before ..." requires all existing data
in the destination container to be moved (i.e. copied) to make space.
SO, instead, we can use "put ... into char x to y of ..." - since it
uses char indexing, it takes constant time (i.e. no scan, just directly
replace the chars. I've attached my complete code so anyone can try it
easily - for my test data of approx 8000 lines, this takes 8 msecs,
versus 588 for the original version.
-- Alex.
on mouseup
put fld "fldout" into tstart
put tstart into ta
repeat 200 times
put tstart after ta
end repeat
put ta into tstart
put the millisecs into t1
put revers(ta) into tb
put the millisecs - t1 & CR after msg
put tstart into ta
put the millisecs into t1
put qrevers(ta) into tc
put the millisecs - t1 & CR after msg
if tb = tc then put "OK" after msg
end mouseup
function revers p
repeat for each line l in p
put L &CR before t
end repeat
return t
end revers
function qrevers p
put p into t
put the number of chars in t into tlen
repeat for each line l in p
put the number of chars in l into tl
put l & cr into char (tLen-tl) to tLen of t
subtract (tl+1) from tLen
end repeat
return t
end qrevers
On 08/02/2015 21:52, J. Landman Gay wrote:
Just tinkering around on a lazy Sunday, and I thought I'd come up with
a neat way to reverse a list without using the traditional clunky method:
function reverseSort pList
repeat for each line l in pList
put l & cr before tList
end repeat
return tList
end reverseSort
One of the best things I learned from a past LC converence came from
Jerry Daniels who said "let the engine do it." It's almost always
faster and more efficient. With that in mind I wrote this:
local sNum
function reverseText pList
put the number of lines in pList into sNum
sort lines of pList numeric by reverseSort(each)
return pList
end reverseText
function reverseSort pTxt
subtract 1 from sNum
return sNum && pTxt
end reverseSort
Works great and I was proud. Then I did some timing tests and found
out the two methods are very close to equivalent in timing, and on
long lists, the first way is actually faster.
So much for improving on LC's text chunking speed. Pah.
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