Randomise items taking rarity into account

totebo

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

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

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

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

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

antix

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="http://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

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