Gammon Forum

-- see: http://en.wikipedia.org/wiki/Fisher-Yates_shuffle


function shuffle(t)
  local n = #t
 
  while n >= 2 do
    -- n is now the last pertinent index
    local k = math.random(n) -- 1 <= k <= n
    -- Quick swap
    t[n], t[k] = t[k], t[n]
    n = n - 1
  end
 
  return t
end

cards = { "Ace", "King", "Queen", "Jack", 10, 9, 8, 7, 6, 5, 4, 3, 2 }

shuffle (cards)

for k, v in ipairs (cards) do
  print (v)
end -- for

Output:

8
9
2
Queen
4
5
7
6
10
Jack
3
Ace
King

  while n > 2 do

  while n >= 2 do

function shuffleArray(array)
    local arrayCount = #array
    for i = arrayCount, 2, -1 do
        local j = math.random(1, i)
        array[i], array[j] = array[j], array[i]
    end
    return array
end

require "copytable"
function shuffleArray(array)
    arrayBackup = copytable.deep(array)
    local arrayCount = #array
    for i = arrayCount, 2, -1 do
        local j = math.random(1, i)
        array[i], array[j] = array[j], array[i]
    end
    return array
end

function unshuffleArray(array)
    return arrayBackup
end

function shuffleArray(array)
    randseed = os.time()
    math.randomseed(randseed)
    local arrayCount = #array
    for i = arrayCount, 2, -1 do
        local j = math.random(1, i)
        array[i], array[j] = array[j], array[i]
    end
    return array
end

function unshuffleArray(array)
    math.randomseed(randseed)
    local arrayCount = #array
    swaps = {}
    for i = arrayCount, 2, -1 do
        table.insert(swaps, {i, math.random(1, i)})
    end
    for i = #swaps,1,-1 do
        array[swaps[i][1]], array[swaps[i][2]] = array[swaps[i][2]], array[swaps[i][1]]
    end
    return array
end