Re: Query: table.sort in 2 or n dim arrays.

[Philippe Lhoste <PhiLho@...>]

John A GILBERT wrote:
> This is a very basic programming query, but I just can't get it worked-out.
> Suppose that there were a 2-d array ( the contents of a simple spreadsheet for example) and one wished to sort a column, say:
> could the table.sort instruction be applied to such an array were it to be defined in the form Array [ x ][y ]?
>
> Any help would be very much appreciated.
> Thank you
>
> John Gilbert.
> (Lua used in scripting an accounting program )

At least a simple question I can answer! -)
An example:

-- Sort a 2D array
local colComp = 3	-- Sort using the third column as criterion
local colComp2 = 2	-- Secondary key
local a =
{
	{ 6, 2, 99, 1 },
	{ 1, 5, 4, 2 },
	{ 4, 47, 74, 3 },
	{ 7, 3, 99, 4 },
	{ 3, 99, 54, 5 },
	{ 8, 47, 101, 6 },
	{ 2, 7, 14, 7 },
	{ 5, 1, 99, 8 },
}

function SimpleSort(el1, el2)
	return el1[colComp] < el2[colComp]
end

function TwoKeySort(el1, el2)
	-- On way to do that is to make a composite key
	local k1 = el1[colComp] * 1000 + el1[colComp2]
	local k2 = el2[colComp] * 1000 + el2[colComp2]
	return k1 < k2
end

function DumpArray()
	for i, t in a do
		for j, st in t do
			io.write(st .. ' ')
		end
		io.write('\n')
	end
end

-- Simple sort (one key)
print("One key sort")
table.sort(a, SimpleSort)
DumpArray()
-- Reset
colComp = 4
table.sort(a, SimpleSort)
colComp = 3
-- Two key sort (two keys)
print("Two key sort")
table.sort(a, TwoKeySort)
DumpArray()

I think you will get the idea with the above code. Otherwise, don't 
hesitate to ask questions.

HTH.

--
Philippe Lhoste
--  (near) Paris -- France
--  Professional programmer and amateur artist
--  http://Phi.Lho.free.fr
--  --  --  --  --  --  --  --  --  --  --  --