Simple sort of table array

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vortizee
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Re: Simple sort of table array

Post by vortizee » Sat Aug 20, 2016 9:02 pm

zorg wrote: When called, table.sort internally calls that sorting function with elements from pcs.A; whether it’s consecutive in order or not, i don't know and frankly don't care, the point is it should sort the table.
I’m just trying to understand how it works so I can write other sorting functions when required. It does sort the table nicely, adding valuable finesse that was missing. As for the nomenclature, I’m an old brain in a new game, so the sequential table made an ambitious stretch of my capabilities easy to reach and understand. Thanks for the explanations, I love you guys. But. . . are you saying my sorting by the third element example (id as a string) in my last post was wrong!?

And ivan, thanks for the cache idea as it reminded me of a number of areas I missed caching that could benefit immensely from it.

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Re: Simple sort of table array

Post by zorg » Sat Aug 20, 2016 9:36 pm

vortizee wrote: But. . . are you saying my sorting by the third element example (id as a string) in my last post was wrong!?
If you mean this:
vortizee wrote:

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table.sort(pcs.A, function (a,b)
  return a[3] < b[3]
end)
I believe that < works on strings too like you'd expect (lexicographically), so it should be good.
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vortizee
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Re: Simple sort of table array

Post by vortizee » Sun Aug 21, 2016 8:28 am

Then I learned something, thanks!

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Positive07
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Re: Simple sort of table array

Post by Positive07 » Sun Aug 21, 2016 6:16 pm

You should also note that, the code you wrote:
vortizee wrote:

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table.sort(pcs.A, function (a,b)
  return a[3] < b[3]
end)
Is sorting the values inside of pcs.A and not those inside pcs. a and b are elements of pcs.A (any two elements) and are expected to be tables since you are indexing them. If you understand this and know what I'm talking about then you have got the idea of how table.sort works!
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vortizee
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Re: Simple sort of table array

Post by vortizee » Mon Aug 22, 2016 4:49 am

Not quite there in a deep sense. I understand what’s happening in these simple sorts, but I’ll be hunting for more complicated examples in the web to gain further understanding. :) My interpretation is that the sort expects pcs.A to be a table to be sorted by the third element of the table (because the function references that index) in ascending order.

If I parse lines w (a table indexed by line number), split each line into a table of 9 elements by a split_by_space function where 3 is an xPosition and 4 is a yPosition, I could sort it as so?

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table.sort ( w, function( a, b )
	return kwikDistance ( a[3], a[4], xo, yo ) < kwikDistance ( b[3], b[4], xo, yo )
end)
If that would work then I’m making progress! Hey, I just discovered the EXPAND VIEW and COLLAPSE VIEW buttons in this forum!

What I could use is a sort of a more complicated structure built as

w[1][1] = { (9 elements where 3 and 4 are an xPos and yPos, and element 6, say, is a size) }
w[1][2] = { ( a table as above) }
w[1][3] = { (ditto) }
w[2][1] = { (ditto) }, w[2][2] = { (ditto) }, w[2][3] = … etc.

First sort by size when w[1] is fully populated before w[2] is created seems simple to do

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table.sort( w[1], function (a,b) return a[6] < b[6] end )
Then sort by distance of w[1][1] versus w[2][1] by the largest elements of each w only, without losing the first sort result

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table.sort( w, function (a,b ) return kwikDistance( a[1][3], a[1][4], xo, yo ) < kwikDistance ( b[1][3], b[1][4] )  end)
Wanting the result where w[1][6] > w[2][6] > w[3][6] … then ordered as w[1]s are nearer to xo, yo than w[2]s and w[2]s nearer than w[3]s as sorted only by the kwikDistance of w[1]. At this point I’m better off testing the output by trial and error. Seems I need a stand-alone interpreter to play with. :roll:

But if the table were to be created without the intermediate sort, and I wanted to sort it all in the end, then it gets even more interesting.

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Re: Simple sort of table array

Post by s-ol » Mon Aug 22, 2016 10:35 am

Is this for a continuous/tile-based map? If your xPositions go from 1 to X and each appears once, and the same happens for yPosition, why use table.sort at all? Just iterate over lines and do

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if not map[xPosition] then map[xPosition] = {} end
map[xPosition][yPosition] = cell
Anyway, if this is not the case your example above looks correct to me.

I would recommend to use string keys wherever you split your lines so your code becomes readable instead of being a confusing mess of [3] and [4]s.

Just set it like

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w[1][1] = { x=12, y=14, size=636... }
This doesn't really impact performance and improves code readability a lot IMO.

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vortizee
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Re: Simple sort of table array

Post by vortizee » Mon Aug 22, 2016 5:02 pm

Thanks, s-ol Not tile based, unfortunately. I have to and do use string keys for the more complicated stuff, but when reading external data by lines I’m only comparing a few data points or building a hash file from it and so split the line by the file delimiter in the simplest way.

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