Randomise items taking rarity into account

totebo · May 2017

I'm building a rarity system, where I have a bunch of items, each with a rarity attached to them, spanning from 1 (common) to 5 (very rare).

To get a random item I create a table with lots of 1s, a bit less of 2s etc and one of each 5. Then table[math.random(#)] that table.

The problem is that this is terribly inefficient, since the table contains hundreds/thousands of items, because I want 1 to be very common and 5 to be very rare indeed.

Is there a better way of doing this?

talis · May 2017

Use simple RPG dice logic;
Roll a dice with 100 sides;
1-40 ----->1 (common item)
40-70 ----->2 (less comon)
70-90 ------> 3 (magical item)
90 - 98 ------> 4 (rare item)
98 - 100 -----> 5 (legendary item)

Note: Change the interval how you want, and arrange the possibility. In addition you can change the rarity possibility easilly by events, like power ups, special magical items.
Sword of luck - Magical property increase chance of finding rare items %5

talis · May 2017

Just for info if you are interested; dungeons and dragons have this method of deciding your talent actions if it succeeds or not and the effect of your action in this way.
1-Event dice - Talent dice (usually 100 sides)
2-Effect dice -Result dice (can change but let us assume 6 sides)

Player wish: I want climb to tree.
Note :Player agility points are so low.
So first we need to decide about the action: Roll a dice and let us assume it is 10 out of 100 .
Hence 10 is so much low it means that there will be a bad consequence of his action and not a successful event. Player can not climb a tree.
Roll a effect dice;
1-3 ---> 3 hp loss
4-5---> 5 hp loss, arm hurts.
6-----> broken leg, unconscious for 2 turns

stetso · May 2017

There is also the weightedchoice() function in lume which I use for a similar task, it works very well for me

you might have to turn around your numbering though because the function will return entries with a higher number more often...
Also, here is some help to design your own probability distribution from dice-rolls. Maybe you can create something that works well for your system.

pie · May 2017

Here I did something similar:
https://github.com/piretro/lua-roulette-wheel/blob/master/rouletteWheel

antix · May 2017

Would just using a random number be wrong???

local items = {
  tier5 = {}, -- best items
  tier4 = {}, -- very good items
  tier3 = {}, -- good items
  tier2 = {}, -- okay items
  tier1 = {}, -- crap items
}
 
local random = math.random
local tier
local r = random()
if r <= 0.05 then -- super fantastic!
  tier = items.tier5
elseif r <= 0.10 then -- pretty good
  tier = items.tier4
elseif r <= 0.20 then -- okay
  tier = items.tier3
elseif r <= 0.50 then -- so so
  tier = items.tier2
else -- haha, you got vendor trash <img class="emoji" src="https://forum.giderosmobile.com/resources/emoji/lol.png" title=":D" alt=":D" height="20" />
  tier = items.tier1
end
 
-- now you have your table of items so choose an item from that table and spawn it

This is how I am choosing pools of item modifications for my ARPG game. It's only just starting to be developed but currently this seems to work pretty well.

totebo · May 2017

Wow guys, amazing responses! This is more than enough for me to make something that works for my game.

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