function for greatest object in list less than or equal to a value

[Peter TB Brett]

Hi Hermann,

There's no array bug -- it's an aspect of its intentional behaviour. 
Appending to an element of an array always causes a copy, so you get 
O(N^2) complexity.

Please re-test in LiveCode 8.0.0-dp-7, because there are some large 
performance optimisations in that release that may affect these results. 
  In particular, I expect anything that uses "put after" outside an 
array to be much faster, and anything that uses sort to be faster (if I 
remember correctly).  This Week in LiveCode has links to the pull 
requests, which explain exactly what's been made faster.

                              Peter

On 13/10/2015 14:42, hh wrote:
> Similar things are useful for a very specialized statistical
> evaluation I have to do soon, so I tested again with LC 7:
>
> There is an interesting difference between LC versions 6 and 7.
>
> The 'direct way' of GC reveals now as clearly fastest.
>
> Tested with one of GC's 12 MB strings on a Mac mini(i5 2.5 GHz),
> testString() as below, and a critical value of v=500000000.
> The (correct) result is 499999246, used time is in seconds.
>
> [a] LC 6.7.7
> repeat-PMB	0.326  <- fastest
> repeat-GC	0.350
> repeat-hh	0.445
> sort-GC		0.985
>
> [b] LC 7.1.0
> repeat-PMB	3.562
> repeat-GC	1.483  <- fastest, the only one with a factor < 9
> repeat-hh      1163.0 <- an ARRAY BUG? :-(
> sort-GC   	8.156
>
> -------------------
>
> function testString
>     set randomseed to 1444826515
>     -- so you'll get exactly my test string
>     repeat 1000000
>        put comma & random(1000000000) after L
>     end repeat
>     delete byte 1 of L
>     return L
> end testString
>
> function repeatPMB L,v  --[1]
>    repeat for each item i in L
>        if i < v then put comma & i after outL
>     end repeat
>     return max(outL)
> end repeatPMB
>
> function repeatGC L,v  --[2]
>     put empty into R
>     repeat for each item i in L
>        if i < v and i > R then put i into R
>     end repeat
>     return R
> end repeatGC
>
> function repeathh L,v  --[3]
>    repeat for each item i in L
>        put comma & i after z[i < v]
>     end repeat
>     return max(z[true])
> end repeathh
>
> function sortGC L,v  --[4]
>     sort items of L descending numeric
>     sort items of L by (each >= v)
>     return item 1 of L
> end sortGC
>
>
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-- 
Dr Peter Brett <peter.brett at livecode.com>
LiveCode Open Source Team

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