Inserting Nil Into Table?

[atrizhong]

Can someone explain why this code does not work for me, and also how to fix it:

local a, b, c, d, e  = "one", "two", "three", "four", "five"; local f, g, h; --Nil values local i, j, k = "six", "seven", "eight" local l, m local t = {a,b,c,d,e,f,g,h,i,j,k,l,m} local nilCounter = 0 print("Size of table: " .. #t); for i = 1, #t do     if (t[i] == nil) then nilCounter = nilCounter + 1 end end print("Number of nil in the table: " .. nilCounter);

Expected Output:

Size of table: 13

Number of nil in the table: 5

Actual Output:

Size of table: 5

Number of nil in the table: 0

For some reason, lua doesn’t seem to recognize the nil values in the table, how would I get it to recognize nil values?

[Joshua_Quick]

Lua tables cannot store nil values.

Lua uses nil to remove table entries instead.  That is, assigning nil to a table entry will remove that entry from the table.

Have a look at the official Lua documentation for this via the link below.

   http://www.lua.org/pil/2.5.html

[atrizhong]

Darn. I was trying to do something like this:

local t = {a,b,c,d,..etc} for i = 1, #t do     if (t[i] == nil) then nilCounter = nilCounter + 1 end end if (nilCounter == 0) then     executeCode(); end

Instead of this:

if (a == nil or b == nil or c == nil or d == nil or e == nil or f == nil or g == nil or h == nil or i ==nil or j == nil or k == nil ...etc) then       executeCode() end

So am I forced to use version b (which may become tedious for long lists) or is it any way possible to achieve version a?

[Joshua_Quick]

Here’s an idea.  How about you create your own “null” type in Lua like this…

   local Null = {}

So, instead of assigning nil to your table entries, you can assign it that “Null” variable and check that instead.

local Null local a, b, c, d, e = "one", "two", "three", "four", "five"; local f, g, h = Null, Null, Null local i, j, k = "six", "seven", "eight" local l, m = Null, Null local t = {a,b,c,d,e,f,g,h,i,j,k,l,m} local nullCounter = 0 print("Size of table: " .. #t); for i = 1, #t do if (t[i] == Null) then nullCounter = nullCounter + 1 end end print("Number of nulls in the table: " .. nullCounter);

[atrizhong]

I cant believe I didn’t think of that. Always learning. Thanks!

[Joshua_Quick]

Happy to help.

Yeah, the only other alternative that I could think of would be to “box” your values in a table, like how you would box primitve types in Java or values types in C#/VB.NET.  Something like this…

local a = { value = "One" } local b = { value = "Two" } local c = {} -- This does not provide a value (ie: stores nil) local myTable = { a, b, c } for index = 1, #myTable then if myTable[index].value == nil then -- Found a nil value. end end

The above is a bit more work and might be a breaking change for you, but if it proves useful, then have at it. 

[Joshua_Quick]

Lua tables cannot store nil values.

Lua uses nil to remove table entries instead.  That is, assigning nil to a table entry will remove that entry from the table.

Have a look at the official Lua documentation for this via the link below.

   http://www.lua.org/pil/2.5.html

[atrizhong]

Darn. I was trying to do something like this:

local t = {a,b,c,d,..etc} for i = 1, #t do     if (t[i] == nil) then nilCounter = nilCounter + 1 end end if (nilCounter == 0) then     executeCode(); end

Instead of this:

if (a == nil or b == nil or c == nil or d == nil or e == nil or f == nil or g == nil or h == nil or i ==nil or j == nil or k == nil ...etc) then       executeCode() end

So am I forced to use version b (which may become tedious for long lists) or is it any way possible to achieve version a?

[Joshua_Quick]

Here’s an idea.  How about you create your own “null” type in Lua like this…

   local Null = {}

So, instead of assigning nil to your table entries, you can assign it that “Null” variable and check that instead.

local Null local a, b, c, d, e = "one", "two", "three", "four", "five"; local f, g, h = Null, Null, Null local i, j, k = "six", "seven", "eight" local l, m = Null, Null local t = {a,b,c,d,e,f,g,h,i,j,k,l,m} local nullCounter = 0 print("Size of table: " .. #t); for i = 1, #t do if (t[i] == Null) then nullCounter = nullCounter + 1 end end print("Number of nulls in the table: " .. nullCounter);

[atrizhong]

I cant believe I didn’t think of that. Always learning. Thanks!

[Joshua_Quick]

Happy to help.

Yeah, the only other alternative that I could think of would be to “box” your values in a table, like how you would box primitve types in Java or values types in C#/VB.NET.  Something like this…

local a = { value = "One" } local b = { value = "Two" } local c = {} -- This does not provide a value (ie: stores nil) local myTable = { a, b, c } for index = 1, #myTable then if myTable[index].value == nil then -- Found a nil value. end end

The above is a bit more work and might be a breaking change for you, but if it proves useful, then have at it.