Author Topic: troubles removing items from a table (Read 2697 times)

Nick · « **on:** May 24, 2012, 03:00:59 pm »

Hi

i'm having trouble with a part of my code

1) a little bit of background information
I'm having a table filled with class instances, from the class cell. each instance has these values:
   - xPos
   - yPos
   - radius
   - xMov
   - yMov

2) every loop i want to remove all the cells with a radius of zero (so self.radius = 0)
as far as i know, i can't do this with a for loop, since removing items out of the table while working with the tablelength in a for loop messes up everything

here's the code

Code: [Select]

cell = class()
cellTable = {}

timer.start(0.01)

function cell:init(x,y,radius)
 self.xPos = x
 self.yPos = y
 self.radius = radius
 self.xMov = math.random(-1,1)
 self.yMov = math.random(-1,1)
end

function on.create()
 text = "no collision"
end

table.insert(cellTable, cell(10,10,10))
table.insert(cellTable, cell(100,90,20))
table.insert(cellTable, cell(69,200,10))
table.insert(cellTable, cell(180,50,10))
table.insert(cellTable, cell(150,150,10))

function on.timer()
 for k,v in pairs(cellTable) do
  v:move()
 end
 removeCells()
 platform.window:invalidate()
end

function on.paint(gc)
 for k,v in pairs(cellTable) do
  v:paint(gc)
 end
 checkCollision(cellTable)
end

function removeCells()
        --here's the part that should remove items out of the list
end

function checkCollision()
        --This function check for collisions (you don't say) and decreases or increases the radius when needed
end

this is only part of the code, but it's the part that matters (it's a school project i'm working on, and should not yet be made available till after the exams)

i hope i made pyself clear, and as always, any help would be greatly appreciated

Nick

Jim Bauwens · « **Reply #1 on:** May 24, 2012, 03:11:32 pm »

Try this:

Code: [Select]

function removeEmpty(tbl)
    for k, v in ipairs(tbl) do
        if v.radius == 0 then
            table.remove(tbl, k)
        end
    end
end

I think that is what you want.

Nick · « **Reply #2 on:** May 24, 2012, 03:24:19 pm »

Perfect, it works like a charm!!!

thanks again jim

Jim Bauwens · « **Reply #3 on:** May 24, 2012, 03:28:40 pm »

I noticed it doesn't work properly at all times, so here is a better function:

Code: [Select]

function removeEmpty(tbl)
    for k, v in ipairs(tbl) do
        if v.radius == 0 then
            table.remove(tbl, k)
            removeEmpty(tbl)
            break
        end
    end
end

It's a bit recursive, so if cellTable is huge (like over 9001 entries), I might need to script an iterative version.

Anyway, glad it works

Edit:
Here is a non recursive function, good if you are handling extremely large amounts of data

Code: [Select]

function removeEmpty(tbl)
    local n = 1
    local rep = true
    while rep do
        rep = false
        for k = n, #tbl do
            if tbl[k].radius == 0 then
                table.remove(tbl, k)
                rep = true
                n = k
                break
            end
        end
    end
end