Question

I just began my adventure with Lua and I’m hitting some issues.

I’ve got a table, which holds instances of object that are use in my application.
I do some stuff with every entry and when I’m done I want to remove it from the table.

Let’s say the scenario is like this:

• create 10 instances and insert them into the table

• do some calculations on some of them [random choice]

• once calculation is done, remove entry from the table

• in the meantime add 10 more instances to the table

• after 6th calculation remove all entries from the table

Since I know how many objects were added from the beginning I am using this count as key of the entry:

table.insert(myTable, tostring(myObject.objectNumber), myObject)

I am using tostring to make sure I don’t run into no key issues [for example, count starts with 0].

I wanted to remove entries using:

table.remove(myTable, tostring(myObject.objectNumber))

But it’s not the key that I have to pass as the second argument but position in the table. This screws the whole idea and I’m a bit lost on how to remove the entry properly without doing a loop over table each time. I cannot see any function which would give me table position of an entry by key.

EDIT:
So the problem is a little bit larger then I thought initially.
First of all:

table.insert(myTable, tostring(0), "something")
assert #myTable == 0

I can see that in my logs:

enemy count:    0
Inserting   0   table: 0x18e8a50
Insert check    0   table: 0x18e8a50
enemy count:    0
Inserting   1   table: 0x18c7c40
Insert check    1   table: 0x18c7c40
enemy count:    1

Also it is not returned by ipairs().

I’m not sure why, but it is how it is.

Second of all,

Inserting   0   table: 0x1781ac60
Insert check    0   table: 0x1781ac60
Inserting   1   table: 0x5e8c20      <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
Insert check    1   table: 0x5e8c20 <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
Inserting   2   table: 0x17807390
Insert check    2   table: 0x17807390
Inserting   3   table: 0x5f5a30
Insert check    3   table: 0x5f5a30
Inserting   4   table: 0x18c7850
Insert check    4   table: 0x18c7850
Inserting   5   table: 0x5e15f0
Insert check    5   table: 0x5e15f0
Inserting   6   table: 0x1784c540
Insert check    6   table: 0x1784c540
Inserting   7   table: 0x5a7b80
Insert check    7   table: 0x5a7b80
Inserting   8   table: 0x18f6d30
Insert check    8   table: 0x18f6d30
Inserting   9   table: 0x189d3e0
Insert check    9   table: 0x189d3e0
remove  0   table: 0x1781ac60
remove check    0   nil 9
Inserting   10  table: 0x18e9c50
Insert check    10  table: 0x18e9c50
Inserting   11  table: 0x5d64a0
Insert check    11  table: 0x5d64a0
Inserting   12  table: 0x19d43540
Insert check    12  table: 0x19d43540
Inserting   13  table: 0x18d5730
Insert check    13  table: 0x18d5730
Inserting   14  table: 0x19d19110
Insert check    14  table: 0x19d19110
Inserting   15  table: 0x595800
Insert check    15  table: 0x595800
Inserting   16  table: 0x5e0f30
Insert check    16  table: 0x5e0f30
remove  5   table: 0x5e15f0
remove check    5   nil 16
remove  4   table: 0x18c7850
remove check    4   nil 16
remove  3   table: 0x5f5a30
remove check    3   nil 16
remove  2   table: 0x17807390
remove check    2   nil 16
remove  6   table: 0x1784c540
remove check    6   nil 16
remove  7   table: 0x5a7b80
remove check    7   nil 16
Inserting   17  table: 0x56fcf0
Insert check    17  table: 0x56fcf0
remove  1   table: 0x5e8c20 <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
remove check    1   nil 17 <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
remove  8   table: 0x18f6d30
remove check    8   nil 17
Inserting   18  table: 0x5970a0
Insert check    18  table: 0x5970a0
remove  9   table: 0x189d3e0
remove check    9   nil 18
Removing all entries:   
1   table: 0x5e8c20     <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
2   table: 0x17807390
3   table: 0x5f5a30
4   table: 0x18c7850
5   table: 0x5e15f0
6   table: 0x1784c540
7   table: 0x5a7b80
8   table: 0x18f6d30
9   table: 0x189d3e0
10  table: 0x18e9c50
11  table: 0x5d64a0
12  table: 0x19d43540
13  table: 0x18d5730
14  table: 0x19d19110
15  table: 0x595800
16  table: 0x5e0f30
17  table: 0x56fcf0
18  table: 0x5970a0
remove  1   table: 0x5e8c20 <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<

As you can see although I have removed the entry earlier, it seems to still be there.
Now.. I thought it was a global-local variable issue with the table, but I’ve added the count of entries to the print [last entry in remove check lines].
The list after “Removing all entries” was created using for loop over pairs(myTable).

Here’s the code where I insert and remove entries:

MyObject = {}
MyObject_mt = { __index = MyObject }

function MyObject:new(params)
    MyObject = {
        objectNumber = params.objectNumber
    }
    local myObject = setmetatable(MyObject, MyObject_mt)

    print("Inserting", tostring(myObject.objectNumber), tostring(myObject))
    table.insert(myTable, tostring(myObject.objectNumber), myObject)
    print("Insert check", tostring(myObject.objectNumber), tostring(myObject))

    function MyObject:removeObject(event)
        print("remove", self.objectNumber, tostring(self))
        myTable[tostring(self.objectNumber)] = nil
        print("remove check", self.objectNumber, tostring(myTable[self.objectNumber]), #myTable)
        end
    end

    return myObject
end

Answer 1

Well assuming you dont have consecutive object numbers (i.e. don’t use the table as an array but rather as a dictionary) you can do simply a

table[tostring(myObject.objectNumber)] = nil;

Thats it, entry removed.