Number Sort Algorithm

[vaporized]

Hello.
I apologize for reviving old thread but forum is already crowded with so many topics I don't want to aggrandize it further.

In mrs. Melanie's routine I don't understand the following:

SortArray:
   ...
   IF CounterA>0 then CounterA=CounterA-2
   ...
   CounterA=CounterA+1
IF CounterA<15 THEN SortArray

As I see it, after the first pass through the loop CounterA is 1, so when it hits IF CounterA>0... wouldn't that make CounterA bigger than15 and exit the loop (CounterA war byte so 1-2=255)?
Can someone please explain it to me?

[Melanie]

>Mrs Melanie!

Don't marry me off yet - I'm having way too much fun being single!

This is a SWAP SORT routine with an Array of 16 elements... (this version is in ASCENDING order, ie the smallest value will end up in RawData(0) and the largest value will end up RawData(15).

First time through the loop CounterA=0 (not 1 as you stated).

You compare RawData(1) with RawData(0) and if RawData(1) is smaller you swap them (NOT if it's bigger or if is the same).

There was an ARRAY BUG in PBP V2.42, which caused problems with Array manipulation - for example RawData(CounterA+1), the workaround (before MeLabs fixed it) was to add a dummy proceedure, so this became RawData(CounterA+1+0). This BUG has long been fixed, so you don't actually need the +0 bit nowadays.

Only if you are NOT at the start of the Array Sort (ie CounterA>0) do you then go back and look at the previous set of Array elements and compare those again (because you've just swapped the upper one of them). You actually subtract 2, because the very next step adds one, so in essence you only go back one Array step. If you are already at the beginning of the Array (ie CounterA=0), you DON'T step back, because that will cause you to step outside your array limits, so you move forward by adding 1 to CounterA.

You repeat the process until you've scanned the whole array and CounterA=15 (your upper Array limit).

So... back to your question...

Whether you SWAP or NOT, if CounterA=0 then the -2 will never happen, you can only move FORWARDS to CounterA=1 (ie CounterA=CounterA+1).

If CounterA=1, then if you DON'T Swap, you move FORWARDS (as above), but if you DO SWAP then CounterA will move BACK by ONE Count (ie CounterA=-2+1), which if CounterA was 1 to start with, it will now move back to be Zero.

[vaporized]

Don't marry me off yet - I'm having way too much fun being single!

Please accept my apology, English is not my native language so I make many mistakes.


Thank you very much for your kind and patient response. Now I see how stupid my question really was. I grasped on CounterA+1 & CounterA-2 as a bull on red flag therefore completely dropping the rest out of my sight. I'll put more effort next time instead of bothering with a silliness.
Thanks again for the explanation, as well for sharing the routine.

Kind regards

[Melanie]

*smiles* No appologies are required!

Doesn't matter about asking questions - that is what this forum is here for, everyone who reads learns something from them.

[aratti]

Well, the way I achieve that is to take say 16 ADC readings, sort them in sequential order of value, junk the top and bottom four readings as being 'out-of-range', sum and average the middle eight... this makes ADC readings in industrial applications pretty much bomb-proof...

Miss Melanie, in doing so you are potentially junking good data, but you can also potentially retain and use in your mean bad data, since you have no way to know how many bad readings you will take with your sampling.

A statistically correct approch should be to calculate the mean and the standard deviation (sd), of all your 16 readings, than retain all data within +/- 1 or 2 sd depending esclusively on your need.

A simpler approach could be to decide which threshold (in percentage of the mean) to apply to reduce the variance, than take the mean of all the 16 readings and discard all the data beyond the threshold limit.

In both cases you will not need to sort your array.

Al.

[Ioannis]

But the maths to do those calculations I feel are more code hungry than just sorting...

Ioannis

[aratti]

Ioannis, if the number that you will display has no importance then you can fix it with a constant, display will be rock stable (always the same number). On the other hand, if the number should provide you usefull information then you must treat it in such a way to preserve those information, which means you must use the correct statistical approch, regardless how code hungry the algorithm could be.

Al.