I'm writing a game using Corona SDK in lua language. I'm having a hard time coming up with a logic for a system like this;
I have different items. I want some items to have 1/1000 chance of being chosen (a unique item), I want some to have 1/10, some 2/10 etc.
I was thinking of populating a table and picking a random item. For example I'd add 100 of "X" item to the table and than 1 "Y" item. So by choosing randomly from [0,101] I kind of achieve what I want but I was wondering if there were any other ways of doing it.
items = {
Cat = { probability = 100/1000 }, -- i.e. 1/10
Dog = { probability = 200/1000 }, -- i.e. 2/10
Ant = { probability = 699/1000 },
Unicorn = { probability = 1/1000 },
}
function getRandomItem()
local p = math.random()
local cumulativeProbability = 0
for name, item in pairs(items) do
cumulativeProbability = cumulativeProbability + item.probability
if p <= cumulativeProbability then
return name, item
end
end
end
You want the probabilities to add up to 1. So if you increase the probability of an item (or add an item), you'll want to subtract from other items. That's why I wrote 1/10 as 100/1000: it's easier to see how things are distributed and to update them when you have a common denominator.
You can confirm you're getting the distribution you expect like this:
local count = { }
local iterations = 1000000
for i=1,iterations do
local name = getRandomItem()
count[name] = (count[name] or 0) + 1
end
for name, count in pairs(count) do
print(name, count/iterations)
end
I believe this answer is a lot easier to work with - albeit slightly slower in execution.
local chancesTbl = {
-- You can fill these with any non-negative integer you want
-- No need to make sure they sum up to anything specific
["a"] = 2,
["b"] = 1,
["c"] = 3
}
local function GetWeightedRandomKey()
local sum = 0
for _, chance in pairs(chancesTbl) do
sum = sum + chance
end
local rand = math.random(sum)
local winningKey
for key, chance in pairs(chancesTbl) do
winningKey = key
rand = rand - chance
if rand <= 0 then break end
end
return winningKey
end
Related
I need to make a trolleybus number, which won't repeat for game. For example, there is a number "101" and there musn't be more "101". How to do that? I have a code, but I know, he won't work and I won't test it lol
function giveNumber()
local number = math.random(100, 199)
local takedNumbers = {}
local i = 0
local massiv = i+1
script.Parent.pered.SurfaceGui.TextLabel.Text = number
script.Parent.zad.SurfaceGui.TextLabel.Text = number
script.Parent.levo.SurfaceGui.TextLabel.Text = number
script.Parent.pravo.SurfaceGui.TextLabel.Text = number
takedNumbers[massiv] = {number}
end
script.Parent.Script:giveNumber() // what I wrote here? idk...
if number == takedNumbers[massiv] then
giveNumber()
end
i didn't test it, because I think it won't work because this code is something bad
I think this will serve your needs.
In the function generateUniqueNumber, the script loops until it found a number that is not yet in the array. (in other words, that it hasn't given out yet)
Once it found that number, it will insert it into the table to remember that it has given it out, and then it will return the number.
Then on the bottom of the script we just give the numbers to the buses :-)
--[[
Goal: Give all buses a unique number
]]
-- Variables
local takenNumbers = {};
-- This function returns a random number in the range [100, 199] that has not been taken yet
function generateUniqueNumber()
local foundNumber = false;
while not foundNumber do
randomNumber = math.random(100, 199);
if not table.find(takenNumbers, randomNumber) then
table.insert(takenNumbers, randomNumber);
return randomNumber;
end
end
end
-- This function sets the number of the bus
script.Parent.pered.SurfaceGui.TextLabel.Text = tostring(generateUniqueNumber());
script.Parent.zad.SurfaceGui.TextLabel.Text = tostring(generateUniqueNumber());
script.Parent.levo.SurfaceGui.TextLabel.Text = tostring(generateUniqueNumber());
script.Parent.pravo.SurfaceGui.TextLabel.Text = tostring(generateUniqueNumber());
2 things:
I didn't test this code as Roblox is not installed on the pc I'm currently on.
Please try formatting your code nicely next time. It greatly improves the readability! For example, you can use this website:
https://codebeautify.org/lua-beautifier
Simpler
Fill a table with free numbers...
local freenumbers = {}
for i = 1, 99 do freenumbers[i] = i + 100 end
...for every new takennumbers use table.remove() on freenumbers
local takennumbers = {}
if #freenumbers > 0 then
takennumbers[#takennumbers + 1] = table.remove(freenumbers, math.random(1, #freenumbers))
end
I have a logic problem for an iOS app but I don't want to solve it using brute-force.
I have a set of integers, the values are not unique:
[3,4,1,7,1,2,5,6,3,4........]
How can I get a subset from it with these 3 conditions:
I can only pick a defined amount of values.
The sum of the picked elements are equal to a value.
The selection must be random, so if there's more than one solution to the value, it will not always return the same.
Thanks in advance!
This is the subset sum problem, it is a known NP-Complete problem, and thus there is no known efficient (polynomial) solution to it.
However, if you are dealing with only relatively low integers - there is a pseudo polynomial time solution using Dynamic Programming.
The idea is to build a matrix bottom-up that follows the next recursive formulas:
D(x,i) = false x<0
D(0,i) = true
D(x,0) = false x != 0
D(x,i) = D(x,i-1) OR D(x-arr[i],i-1)
The idea is to mimic an exhaustive search - at each point you "guess" if the element is chosen or not.
To get the actual subset, you need to trace back your matrix. You iterate from D(SUM,n), (assuming the value is true) - you do the following (after the matrix is already filled up):
if D(x-arr[i-1],i-1) == true:
add arr[i] to the set
modify x <- x - arr[i-1]
modify i <- i-1
else // that means D(x,i-1) must be true
just modify i <- i-1
To get a random subset at each time, if both D(x-arr[i-1],i-1) == true AND D(x,i-1) == true choose randomly which course of action to take.
Python Code (If you don't know python read it as pseudo-code, it is very easy to follow).
arr = [1,2,4,5]
n = len(arr)
SUM = 6
#pre processing:
D = [[True] * (n+1)]
for x in range(1,SUM+1):
D.append([False]*(n+1))
#DP solution to populate D:
for x in range(1,SUM+1):
for i in range(1,n+1):
D[x][i] = D[x][i-1]
if x >= arr[i-1]:
D[x][i] = D[x][i] or D[x-arr[i-1]][i-1]
print D
#get a random solution:
if D[SUM][n] == False:
print 'no solution'
else:
sol = []
x = SUM
i = n
while x != 0:
possibleVals = []
if D[x][i-1] == True:
possibleVals.append(x)
if x >= arr[i-1] and D[x-arr[i-1]][i-1] == True:
possibleVals.append(x-arr[i-1])
#by here possibleVals contains 1/2 solutions, depending on how many choices we have.
#chose randomly one of them
from random import randint
r = possibleVals[randint(0,len(possibleVals)-1)]
#if decided to add element:
if r != x:
sol.append(x-r)
#modify i and x accordingly
x = r
i = i-1
print sol
P.S.
The above give you random choice, but NOT with uniform distribution of the permutations.
To achieve uniform distribution, you need to count the number of possible choices to build each number.
The formulas will be:
D(x,i) = 0 x<0
D(0,i) = 1
D(x,0) = 0 x != 0
D(x,i) = D(x,i-1) + D(x-arr[i],i-1)
And when generating the permutation, you do the same logic, but you decide to add the element i in probability D(x-arr[i],i-1) / D(x,i)
I want to randomly populate a grid in Lua using a list of possible items, which is defined as follows:
-- Items
items = {}
items.glass = {}
items.glass.color = colors.blue
items.brick = {}
items.brick.color = colors.red
items.grass = {}
items.grass.color = colors.green
So the keys of the table are "glass", "brick" and "grass".
How do I randomly select one of these keys if they are not addressable by a numeric index?
Well, I kind of got a workaround, but I would be open to any better suggestions.
The first solution consists of having a secondary table which serves as an index to the first table:
item_index = {"grass", "brick", "glass"}
Then I can randomly store a key of this table (board is a matrix that stores the value of the random entry in item_index):
local index = math.random(1,3)
board[i][j] = item_index[index]
After which I can get details of the original list as follows:
items[board[y][x]].color
The second solution, which I have decided on, involves adding the defined elements as array elements to the original table:
-- Items
items = {}
items.glass = {}
items.glass.color = colors.blue
table.insert(items, items.glass) --- Add item as array item
items.brick = {}
items.brick.color = colors.red
table.insert(items, items.brick) --- Add item as array item
items.grass = {}
items.grass.color = colors.green
table.insert(items, items.grass) --- Add item as array item
Then, I can address the elements directly using an index:
local index = math.random(1,3)
board[i][j] = items[index]
And they can be retrieved directly without the need for an additional lookup:
board[y][x].color
Although your second method gives concise syntax, I think the first is easier to maintain. I can't test here, but I think you can get the best of both, won't this work:
local items = {
glass = {
color = colors.blue,
},
brick = {
color = colors.red,
},
grass = {
color = colors.green,
},
}
local item_index = {"grass", "brick", "glass"}
local index = math.random(1,3)
board[i][j] = items[item_index[index]]
print('color:', board[i][j].color)
If you're table is not too big and you can just break off at a random point. This method assumes that you know the number of entries in the table (which is not equal to #table value, if the table has non-number keys).
So find the length of the table, then break at random(1, length(table)), like so:
local items = {} ....
items.grass.color = colors.green
local numitems = 0 -- find the size of the table
for k,v in pairs(items) do
numitems = numitems + 1
end
local randval = math.random(1, numitems) -- get a random point
local randentry
local count = 0
for k,v in pairs(items) do
count = count + 1
if(count == randentry) then
randentry = {key = k, val = v}
break
end
end
The goods: You don't have to keep track of the keys. It can be any table, you don't need to maintain it.
The bad and ugly: It is O(n) - two linear passes.So, it is not at all ideal if you have big table.
The above answers assume you know what all of the keys are, which isn't something I was able to do earlier today. My solution:
function table.randFrom( t )
local choice = "F"
local n = 0
for i, o in pairs(t) do
n = n + 1
if math.random() < (1/n) then
choice = o
end
end
return choice
end
Explanation: we can't use table.getn( t ) to get the size of the table, so we track it as we go. The first item will have a 1/1=1 chance of being picked; the second 1/2 = 0.5, and so on...
If you expand for N items, the Nth item will have a 1/N chance of being chosen. The first item will have a 1 - (1/2) - (1/3) - (1/4) - ... - (1/N) chance of not being replaced (remember, it is always chosen at first). This series converges to 1 - (N-1)/N = 1/N, which is equal to the chance of the last item being chosen.
Thus, each item in the array has an equal likelihood of being chosen; it is uniformly random. This also runs in O(n) time, which isn't great but it's the best you can do if you don't know your index names.
I was working on a script to randomize the data inside of my array but I get and error
that says
unexpected symbol near "#"
When I go to that line, and I remove the "#" I get
attempt to perform arithmetic on local `n' (a table value)
Here is my shuffle function
function shuffle(array)
local array = array
local n = #array
local j
local random = math.random
for i=n-1, 1, -1 do
j = random(i)
array[j],array[i] = array[i],array[j]
end
return array
end
and here is what I am trying to randomize
shuffle(new_players)
for name,character in pairs(new_players) do
if (character.inside == true and character.death == 0) then
local player = getPlayerByName(name, map_copy)
if (player ~= nil) then
addState(player)
break
end
end
end
Here is my array
new_players= { }
new_players[charName] = { death = 0, inside= true }
Any help? If i am doing something completely wrong?
1) Try change charName from string to a number.
2) For shuffle you can use this code:
function swap(array, index1, index2)
array[index1], array[index2] = array[index2], array[index1]
end
function shuffle(array)
local counter = #array
while counter > 1 do
local index = math.random(counter)
swap(array, index, counter)
counter = counter - 1
end
end
If your Lua version is < 5.1 then there is no # operator. Use table.getn instead:
local n = table.getn(array);
(Update) Note that your function, while it does shuffle the items around, it does not really shuffle all elements. Also since you reduce the range with each iteration, you will almost certainly swap the first 10% of your array around multiple times. Now swapping them multiple times is not bad by itself, but that you are, by comparison, almost never swapping the other elements is.
So one option to solve this would be to always use the same range for your random variable. And I would go even further and select two random indexes to swap:
function shuffle(array)
local n, random, j = table.getn(array), math.random
for i=1, n do
j,k = random(n), random(n)
array[j],array[k] = array[k],array[j]
end
return array
end
The other option would be to select random elements from the source array and put them into a new output array:
local rnd,trem,getn,ins = math.random,table.remove,table.getn,table.insert;
function shuffle(a)
local r = {};
while getn(a) > 0 do
ins(r, trem(a, rnd(getn(a))));
end
return r;
end
Being fairly new to Stata, I'm having a difficulty figuring out how to do the following:
I have time-series data on selling price (p) and quantity sold (q) for 10 products in a single datafile (i,e., 20 variables, p01-p10 and q01-q10). I am strugling with appropriate stata command that computes sales revenue (pq) time-series for each of these 10 products (i.e., pq01-pq10).
Many thanks for your help.
forval i = 1/10 {
local j : display %02.0f `i'
gen pq`j' = p`j' * q`j'
}
A standard loop over 1/10 won't get you the leading zero in 01/09. For that we need to use an appropriate format. See also
#article {pr0051,
author = "Cox, N. J.",
title = "Stata tip 85: Looping over nonintegers",
journal = "Stata Journal",
publisher = "Stata Press",
address = "College Station, TX",
volume = "10",
number = "1",
year = "2010",
pages = "160-163(4)",
url = "http://www.stata-journal.com/article.html?article=pr0051"
}
(added later) Another way to do it is
local j = string(`i', "%02.0f")
That makes it a bit more explicit that you are mapping from numbers 1,...,10 to strings "01",...,"10".