Lua weird behavior on lua table size.

[drakylucas]

Hi all,

I don't know if it should be in support, or discussion

why does lua have this weird behavior?

local table0 = {}

local table1 = {
[0] = "xx",
}

local table2 = {
[1] = "xx",
}

local table3 = {
[0] = "xx",
[1] = "yy",
}

local table4 = {
[0] = "xx",
[1] = "yy",
[2] = "yy",
}

local table5 = {
[1] = "xx",
[2] = "yy",
[3] = "yzy",
}

print("table0: " ..#table0)
print("table1: " ..#table1)
print("table2: " ..#table2)
print("table3: " ..#table3)
print("table4: " ..#table4)
print("table5: " ..#table5)

this will print this out:

table0: 0
table1: 0
table2: 1
table3: 1
table4: 2
table5: 3

if the table has an item with index "[0]", it is not counted in tablesize (using "#" symbol)
is there any reason for this to happen?
I'm just curious.

 

[Xikini]

Hi all,

I don't know if it should be in support, or discussion

why does lua have this weird behavior?

local table0 = {}

local table1 = {
[0] = "xx",
}

local table2 = {
[1] = "xx",
}

local table3 = {
[0] = "xx",
[1] = "yy",
}

local table4 = {
[0] = "xx",
[1] = "yy",
[2] = "yy",
}

local table5 = {
[1] = "xx",
[2] = "yy",
[3] = "yzy",
}

print("table0: " ..#table0)
print("table1: " ..#table1)
print("table2: " ..#table2)
print("table3: " ..#table3)
print("table4: " ..#table4)
print("table5: " ..#table5)

this will print this out:


if the table has an item with index "[0]", it is not counted in tablesize (using "#" symbol)
is there any reason for this to happen?
I'm just curious.

Lua arrays start at 1 instead of 0.

You can technically start them at any number you want, but some standard functions become unreliable if the index doesn't start at 1.

Programming in Lua : 11.1

 

[drakylucas]

The interesting thing is:

print(table1[0])

shows "xx"

so lua knows that there is something on index 0, but it doesn't count on counting table elements (#table1 returns 0)

 

[River KA]

Hi all,

I don't know if it should be in support, or discussion

why does lua have this weird behavior?

local table0 = {}

local table1 = {
[0] = "xx",
}

local table2 = {
[1] = "xx",
}

local table3 = {
[0] = "xx",
[1] = "yy",
}

local table4 = {
[0] = "xx",
[1] = "yy",
[2] = "yy",
}

local table5 = {
[1] = "xx",
[2] = "yy",
[3] = "yzy",
}

print("table0: " ..#table0)
print("table1: " ..#table1)
print("table2: " ..#table2)
print("table3: " ..#table3)
print("table4: " ..#table4)
print("table5: " ..#table5)

this will print this out:


if the table has an item with index "[0]", it is not counted in tablesize (using "#" symbol)
is there any reason for this to happen?
I'm just curious.

The # keyword is to count values between 1 to "n".

---

If you want to count all elements within a table, independently of the keys, you should keep it registered in another location (if need too much efficiency).

If you don't need it (which is probably), you can simply use a common table function:

function table.size(t)
  local size = 0
  for _, _ in pairs(t) do
    size = size + 1
  end
  return size
end

See this example:

local t =
{
  0, -- [1] = 0
  1, -- [2] = 1
  nil, -- Does not count! -- [3] = nil
  'hello!!', -- [4] = 'hello!!'

  [_t] = 'msg', -- [table_reference] = 'msg'

  hi = 'hi', -- ['hi'] = 'hi'
  ['hiho!'] = 'hiho!', -- ['hiho!'] = 'hiho!'

  [7] = 7, -- [7] = 7
  [-1] = -1, -- [-1] = -1
}

print(table.size(t)) -- Prints 8 (since nil does not count)