Shorting table values by alphabetic order

[jaliborc]

How can I short table values by alphabetic order? I want to save values with a given id, and then short them by id alphabetic order. Here is a example:

local table = {}

local function addLine(id, value)
  table[id] = value
end

addLine('Apple', {name = 'CrazyApple', otherValue = 'example'}
addLine{'Banana', {name = 'StupidBanana', someValue = 'example'}
addLine{'Strawberry', {name = 'Mania Strawberry', oneValue = 'example'}

for k,v in pairs(table) do
  --some function
end

The problem is with the last three lines. I'm sure there is a way to short the values by the correct order, but I don't know how.

[Slakah]

By short do you mean sort?

[Akryn]

local function f (a, b)
--return true if a comes before b alphabetically
end

table.sort(table, f)

[jaliborc]

Originally Posted by Slakah By short do you mean sort?

Yes, sorry, I'm not a native English speaker.

Originally Posted by Akryn local function f (a, b) --return true if a comes before b alphabetically end table.sort(table, f)

I will try that. Thanks!

EDIT: How can I know if a comes before b? Would using strbyte work?

[Akryn]

yeah -- i've never had to do this in lua, but here's what i came up with off the top of my head (untested)

local function f(a, b)
    a, b = strlower(a), strlower(b)
    for i = 1, strlen(a) do
        local c1, c2 = strbyte(a, i), strbyte(b, i)
        if c1 and c2 then
             if c1 ~= c2 then
                 return c1 < c2
             end
        elseif c1 then
             return false
        end
    end
end

[Layrajha]

I haven't tested it, but I'd assume that the basic "<" operator is the alphabetical order, when used to compare strings. Thus, doing

table.sort(table)

would work, or if you want to use table.sort(table, f), you could define

function f(a,b)
  return a<b
end

or

function f(a,b)
  if a<b then
    return true
  else 
    return false
end

(but it's ugly)

[jaliborc]

Originally Posted by Layrajha I haven't tested it, but I'd assume that the basic "<" operator is the alphabetical order, when used to compare strings. Thus, doing table.sort(table) would work, or if you want to use table.sort(table, f), you could define function f(a,b) return a<b end

I think Lua can't compare string values with "<". strbyte is required to turn them in numbers

[jaliborc]

Originally Posted by Akryn yeah -- i've never had to do this in lua, but here's what i came up with off the top of my head (untested) local function f(a, b) a, b = strlower(a), strlower(b) for i = 1, strlen(a) do local c1, c2 = strbyte(a, i), strbyte(b, i) if c1 and c2 then if c1 ~= c2 then return c1 < c2 end elseif c1 then return false end end end

Thanks again! I already have an idea how to do it. It should be close to your code with some minor changes.

[Layrajha]

Originally Posted by jaliborc I think Lua can't compare string values with "<". strbyte is required to turn them in numbers

Just tested it because I was almost sure that it worked, and indeed, it works

[jaliborc]

Originally Posted by Layrajha Just tested it because I was almost sure that it worked, and indeed, it works

Even better!

[jaliborc]

I don't know why, but the function "sort" isn't working. Calling it is the same as doing nothing. The #2 arg (a function) is not even called.

EDIT: Appears that the sort function only works with number indexes. I was looking for some way to sort the table with string indexes. Any ideas?

[Akryn]

Originally Posted by jaliborc I don't know why, but the function "sort" isn't working. Calling it is the same as doing nothing. The #2 arg (a function) is not even called. EDIT: Appears that the sort function only works with number indexes. I was looking for some way to sort the table with string indexes. Any ideas?

what functionality are you looking for? string-indexed tables are unsorted almost by definition, since the keys themselves aren't logically sequential. if you're looking to sort the *keys* so that foreach or pairs gives them to you alphabetically, that's not going to happen because those functions go by the actual lua back-end table order, which may as well be random.

the best thing to do may be to get rid of the string keys, replace the current values with tables in the form {"old key", old value}, and then just sort it by "old key"

[jaliborc]

Originally Posted by Akryn if you're looking to sort the *keys* so that foreach or pairs gives them to you alphabetically, that's not going to happen because those functions go by the actual lua back-end table order, which may as well be random.

That's why I created this thread: to know if anyone knew a way (complex or not) to short them by key values in alphabetic order.

[jaliborc]

Thanks guys, but I already found a way to sort the values in alphabetic order. Is a bit complex, but it works.