How to random collection from Index Switch Node by mesh island index?

Question

I have a mesh that contains more than 100 mesh islands and 10 groups, each containing 100 collections of assets that I want to array to these mesh borders. I use the Switch Index Node to get the combination options of the instance.

I'm trying to get the random options for the combination that was instanced to each mesh island instead of a specific option for all islands. But the switch index seems like don't work with random node.

Let's take a look at a simple example with a mesh that contains 3 islands: And 3 groups with 7 collections of instance:

• Group Blank: 1 collection
• Group A: 3 collections
• Group B: 3 collections

The current node setup just gets a specific combination index (1-1-1, 1-2-1, 1-3-2,...) for all islands.

Have any idea how to get the random combination index for each island?

Like 1-1-1 for island 1, 1-2-1 for island 2, and so on.

Remember, this will be used to address a mesh with over 100 islands and 10 groups, each containing 100 collections.

I don't want to make the combination options of these collections manually. So using the random method will be helpful.

Get more details from the example blender file (Version 4.3) below.

Answer 1

The problem you are facing is that a Random Value node will have a "field" output if ID or Seed are also "fields". You need to apply a constant value to both inputs to get a constant output.

The idea I am going to demonstrate can be described as follows:

1. Interact with each spline separately using a For Each Element zone.

2. Randomize each collection independently of each other and independently of the spline groups:

• For each Random value node, the ID is set to the ID of each spline to ensure that the values ​​are independent for each "spline".

• Each Random value node has a different Seed value to ensure that all random nodes are independent of each other. To do this, I simply add 1 to each Seed of the next node

• Finally, I multiply by the number of collections of the input Seed to make sure there are no dependencies of Random Value nodes ​​for different input seeds. Why do this? Let's assume like in the example you gave that there are 3 collections. Now, for the first spline (ID = 0 for each Random value), if I didn't use this multiplication: For Seed = 0 seeds are (0, 1, 2). For Seed = 1 seeds are (1, 2, 3). So 1 and 2 will be repeated again for Seed = 1 for the same spline. You might not even notice this, but I wanted to also get values ​​independent of each seed, so I do this multiplication. So what I did was: Seed = 0 : 0 times 3 = 0, seeds are (0, 1, 2). For Seed = 1: 1 times 3 = 3, so seeds are (3, 4, 5). No interference now.

Note: if you know you have 100 collections, you can just multiply Seed by 100 directly, then there is no need to use Domain Size.

My only concerns are:

1. Are they really independent? I think so, but maybe not, maybe I'm missing something.
2. The For Each Element zone is "quite slow", overall I wouldn't recommend using it if you can avoid it. Only use it if it doesn't have a huge impact on performance or you really can't solve the problem without it.

The entire code block:

Result:

Answer 2

A proper solution is to join all objects into a single group, then use "pick instances" to pick the right one, based on some mapping:

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Tested on:

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Result:

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