Algorithm time...

[Richard Gaskin]

Glen Bojsz wrote:

 > Once again I hope the algorithm experts can speed of the following...
 > currently on just 50,000 points it takes 10 seconds ...as I indicate
 > below I know why so this is why I am looking for better solutions
...
 >*on* mouseUp
 >   *put* the seconds into startTime
 >   *put* the number of lines of fld mydataNew into tcount
 >   *put* fld mydataNew into gbmem
 >   *put* tcount / 1000 into tgroup
 >   *put* 0 into x
 >   *put* 1 into y
 >   *repeat* for 1000 times
...
 >      *put* line startline to endline of gbmem into grptest

There are a few opportunities for optimization here, and if it had been 
pasted as plain text so I could work with it without having to first 
clean it up I might have done a quick rewrite.

But to get you started, the last two lines as excerpted above are important.

If you switch the repeat to use the "repeat for each line..." form 
you'll get about an order of magnitude performance boost.

The issue is that "repeat <n>" doesn't know if the data being counted 
may have changed, so when you later ask to go to line "startLine" each 
time through the loop it starts counting at 1 and continues down to 
startLine every iteration.  This is a lot of redundant processing, and 
as you can guess gets progressively slower as you work your way through 
the data set.

The "repeat for each" form has the limitation that you cannot alter the 
data being stepped through, but with that assumption is able to deliver 
radically improved performance because it parses out the next line and 
keeps its place in the data step each time through the loop, allowing 
performance to scale linearly.

There are a few other things you might consider optimizing in that 
handler, but once you get the switch to "repeat for each" worked out I 
suspect you'll be so happy with the performance you'll move on to other 
things. :)

--
  Richard Gaskin
  Fourth World Systems
  Software Design and Development for Desktop, Mobile, and Web
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