Lua - 排序表并随机化关系

Question

I have a table with two values, one is a name (string and unique) and the other is a number value (in this case hearts ). What I want is this: sort the table by hearts but scramble randomly the items when there is a tie (eg hearts is equal). By a standard sorting function, in case of ties the order is always the same and I need it to be different every time the sorting function works. This is anexample:

tbl = {{name = "a", hearts = 5}, {name = "b", hearts = 2}, {name = "c", hearts = 6}, {name = "d", hearts = 2}, {name = "e", hearts = 2}, {name = "f", hearts = 7}}
sort1 = function (a, b) return a.hearts > b.hearts end
sort2 = function (a, b)
    if a.hearts ~= b.hearts then return a.hearts > b.hearts
    else return a.name > b.name end
end

table.sort(tbl, sort2)

local s = ""
for i = 1, #tbl do
    s = s .. tbl[i].name .. "(" .. tbl[i].hearts .. ") "
end
print(s)

Now, with the function sort2 I think I quite got the problem. The problem is, what happens when a.hearts == b.hearts ? In my code it just orders the ties by their name, not what I want. I have two ideas:

1. First scramble randomly all the items in the table, then apply sort1 .
2. Add a value to every element of the table, called rnd , that is a random number. Then in sort2 , when a.hearts == b.hearts order the items by a.rnd > b.rnd .
3. In sort2 , when a.hearts == b.hearts generate randomly true or false and return it. It doesn't work, and I understand that this happens because the random true/false makes the order function crash since there could be inconsistencies.

I don't like 1 (because I would like to do everything inside the sorting function) and 2 (since it requires to add a value), I would like to do something like 3 but working. The question is: is there a way do to this in a simple manner, and what is an optimal way of doing this? (maybe, method 1 or 2 are optimal and I don't get it).

Bonus question. Moreover, I need to fix an item and sort the others. For example, suppose we want "c" to be first. Is it good to make a separate table with only the items to sort, sort the table and then add the fixed items?

Answer 1

-- example table
local tbl = {
  { name = "a", hearts = 5 },
  { name = "b", hearts = 2 },
  { name = "c", hearts = 6 },
  { name = "d", hearts = 2 },
  { name = "e", hearts = 2 },
  { name = "f", hearts = 7 },
}

-- avoid same results on subsequent requests
math.randomseed( os.time() )

---
-- Randomly sort a table
--
-- @param tbl Table to be sorted
-- @param corrections Table with your corrections
--
function rnd_sort( tbl, corrections )
   local rnd = corrections or {}
   table.sort( tbl,
      function ( a, b)
         rnd[a.name] = rnd[a.name] or math.random()
         rnd[b.name] = rnd[b.name] or math.random()
         return a.hearts + rnd[a.name] > b.hearts + rnd[b.name]
      end )
end

---
-- Show the values of our table for debug purposes
--
function show( tbl )
   local s = ""
   for i = 1, #tbl do
       s = s .. tbl[i].name .. "(" .. tbl[i].hearts .. ") "
   end
   print(s)
end

for i = 1, 10 do
   rnd_sort(tbl)
   show(tbl)
end

rnd_sort( tbl, {c=1000000} )  -- now "c" will be the first
show(tbl)

Answer 2

Here's a quick function for shuffling (scrambling) numerically indexed tables:

function shuffle(tbl) -- suffles numeric indices
    local len, random = #tbl, math.random ;
    for i = len, 2, -1 do
        local j = random( 1, i );
        tbl[i], tbl[j] = tbl[j], tbl[i];
    end
    return tbl;
end

Answer 3

If you are free to introduce a new dependency, you can use lazylualinq to do the job for you (or check out how it sorts sequences, if you do not need the rest):

local from = require("linq")

math.randomseed(os.time())

tbl = {{name = "a", hearts = 5}, {name = "b", hearts = 2}, {name = "c", hearts = 6}, {name = "d", hearts = 2}, {name = "e", hearts = 2}, {name = "f", hearts = 7}}

from(tbl)
    :orderBy("x => x.hearts")
    :thenBy("x => math.random(-1, 1)")
    :foreach(function(_, x) print(x.name, x.hearts) end)