How does one reverse the items in a table in Lua?

Question

Is there something that would do the same thing as table.sort, but backwards?

Does this answer your question? [sorting a table in descending order in Lua](https://stackoverflow.com/questions/6726130/sorting-a-table-in-descending-order-in-lua) — mrjamaisvu, Jun 28 '22 at 08:58
Have you take a look at [this post](https://stackoverflow.com/questions/6726130/sorting-a-table-in-descending-order-in-lua)? — mrjamaisvu, Jun 28 '22 at 08:59
Do you want to _"sort a table in reverse order"_ or _"just reverse the items in a table"_? Those are completely different things. — Zakk, Jun 28 '22 at 09:22

user19433446 · Answer 1 · 2022-06-28T09:27:48.407

The table.sort function allows you to define a sorting function as the second argument. It returns a boolean and specifies the order on which the table must be ordered:

local atable = {1,2,3}
table.sort(atable, function(a,b) return a > b end)
for _, v in pairs(atable) do
    print(v)
end
--[[This prints:
3
2
1
]]

Of course, this doesn't limit itself to "lists" but you can use them on other table types as well:

local cityInfo = {
{name = "Vancouver", population = 321, location = "Canada"},
{name = "Paris", population = 123, location = "France"},
{name = "London", population = 1000, location = "United Kingdom"},
}
table.sort(cityInfo, function(a,b) return a.population > b.population end) -- Here the items are ordered in descencing order based on the population field
for _, v in pairs(cityInfo) do
    print(v.population)
end
--[[This prints:
1000
321
123
]]

"Of course, this doesn't limit itself to "lists" but you can use them on other table types as well" - this is plain wrong. `table.sort` **is literally limited to the list part of the table**. Your first table is a "list" of primitive values (numbers) whereas your second table is a "list" of tables. Both are lists. — Luatic, Jun 28 '22 at 09:49

score 0 · Answer 2 · answered Jun 28 '22 at 10:03

If you want to sort a table in reverse order:

table.sort(your_table, function(x, y) return x > y end)

If you want to reverse a table:

local function reverse(tab)
    for i = 1, #tab//2, 1 do
        tab[i], tab[#tab-i+1] = tab[#tab-i+1], tab[i]
    end
    return tab
end

How does one reverse the items in a table in Lua?

2 Answers2