Loot Tables for Minable Entities

[someloser]

Minable Entities with loot tables that contain multiple entries with a probability value that is less-than 1 don't work the way you expect them to. A table with 5 entries with each item having a 20% chance to drop doesn't guarantee a loot drop every time. In fact, this set-up will only drop loot 67.2% of time.

Each entry has it's own chance to drop, they are independent events. If the chance to drop was 50% instead of 20%, it would be flipping 5 different coins, and if that coin came up "heads" that item would drop. Since 5 coins can fall all as "tails", when that happens no loot will drop.

To find out the chance of no loot dropping overall, you multiply the individual chances of that item not dropping together.

So if the individual chances were (10%, 10%, 10%, 30%, 40%), nothing would drop 30.6% of the time. (0.9 * 0.9 * 0.9 * 0.7 * 0.6 == 0.30618)


note: This is the behaviour I've noticed on minable entities only. The loot tables of enemies might work differently.

[Platoonsgt1]

Does this mean that there is a probability that you'll get multiple ores at once, or does getting one ore cancel the chances of you getting others?

In different words, if you went (10%, 10%, 20%, 40%, 100%), would you get the last ore only when you didn't get the others, or would you get the last ore as well as a random assortment of the others?

[muzzy]

I like the idea of some resource fields giving mixed set of ore. Forcing players to use smart inserters sounds good

[someloser]

Does this mean that there is a probability that you'll get multiple ores at once, or does getting one ore cancel the chances of you getting others?

In different words, if you went (10%, 10%, 20%, 40%, 100%), would you get the last ore only when you didn't get the others, or would you get the last ore as well as a random assortment of the others?

I've just done some testing with (50%, 50%, 100%) and it seems you do get the 100% every time EXCEPT when the two at 50% drop together.

Testing at (99%, 99%, 99%, 100%) confirmed that it only uses the first two successful drops, any latter drops are discarded, no matter their probability value. So if you want to force a drop every time, put that entry first.

[Schmendrick]

I've just done some testing with (50%, 50%, 100%) and it seems you do get the 100% every time EXCEPT when the two at 50% drop together.

Testing at (99%, 99%, 99%, 100%) confirmed that it only uses the first two successful drops, any latter drops are discarded, no matter their probability value. So if you want to force a drop every time, put that entry first.

I don't think this is the whole story. Scrapmod clearly works with multiple drops. I wondered if something changed in 0.10, so I fired it up and scrapped a bunch of assembler-3's.

The generated loot table (for the current, not-uploaded-yet version) is:

0-2 speed module
55% chance of 1 assembler-2
0-3 advanced circuit
0-7 electric circuit
0-9 iron plate
0-2 iron gear
1-3 plastic
1-11 copper cable
1-4 iron ore
77% chance of 1 copper plate
44% chance of 1 copper ore

The results:

assembly3scrap.png (326.08 KiB) Viewed 6484 times

As you can see, in (at least) one instance, every item triggered.