# Agents.jl - @multiagent : MethodError: Cannot \`convert\` an object of type People to an object of type Family
**URL:** https://discourse.julialang.org/t/agents-jl-multiagent-methoderror-cannot-convert-an-object-of-type-people-to-an-object-of-type-family/114466
**Category:** Specific Domains
**Tags:** agents
**Created:** [May 20, 2024, 6:11am UTC](https://discourse.julialang.org/t/agents-jl-multiagent-methoderror-cannot-convert-an-object-of-type-people-to-an-object-of-type-family/114466 "2024-05-20T06:11:41Z")
**Posts on this page:** 6
**Page:** 1
### Author:  [@imantha](https://discourse.julialang.org/u/imantha)
#### Post date: [May 20, 2024, 6:11am UTC](https://discourse.julialang.org/t/agents-jl-multiagent-methoderror-cannot-convert-an-object-of-type-people-to-an-object-of-type-family/114466/1 "2024-05-20T06:11:41Z")
I am a little clueless on how to use @multiagent macro in Agents.jl. For the problem I am trying to solve there are multiple agents and I am trying to add each as subagent but I get the error : `MethodError: Cannot `convert` an object of type People to an object of type Family`. Any idea how to fix this
```julia
@multiagent struct People(GraphAgent)
@subagent struct Person
age::Integer
health_condition::Float32
gender::Integer
family::Family
end
@subagent struct Family
number_of_members::Int
end
end
Person(1,1,32,0.5,1, Family(1,1,5))
>>> MethodError: Cannot convert ...
```
---
### Author:  [@nivertech](https://discourse.julialang.org/u/nivertech)
#### Post date: [May 20, 2024, 9:09am UTC](https://discourse.julialang.org/t/agents-jl-multiagent-methoderror-cannot-convert-an-object-of-type-people-to-an-object-of-type-family/114466/2 "2024-05-20T09:09:46Z")
1. Multiagent agent types are not a real Julia types, they are just symbols - “kinds”. It described in the docs.
```julia
kindof(Person(...)) = :Person
kindof(Family(...)) = :Family
allkinds(People) = [:Person, :Family]
```
> **[API · Agents.jl](https://juliadynamics.github.io/Agents.jl/stable/api/#Agents.%40multiagent)**
>
> Documentation for Agents.jl.
1. What is your Graph space? Is it a family relationships network?
If yes, then you don’t need a `family` attribute in the `Person` subagent.
If the graph space is unrelated to family relationships, then you can create a separate graph as a property of the model and/or agents using Garphs.jl as in the School Yard example:
> **[Graphs.jl · Agents.jl](https://juliadynamics.github.io/Agents.jl/stable/examples/schoolyard/)**
>
> Documentation for Agents.jl.
1. If you want to keep things simple and don’t need an actual graph space or graph model/agent property, then you can just store an integer agent id of the Family subagent in the Person subagent, i.e. when initializing the agents, you will need to create `Family` agent first, and then create all the corresponding `Person` agents as members of the same `Family`.
---
### Author:  [@imantha](https://discourse.julialang.org/u/imantha)
#### Post date: [May 20, 2024, 11:36am UTC](https://discourse.julialang.org/t/agents-jl-multiagent-methoderror-cannot-convert-an-object-of-type-people-to-an-object-of-type-family/114466/3 "2024-05-20T11:36:59Z")
Thanks that probably works. Its a covid model and actually I am borrowing some ideas from an open source model called Pyfectious to some what change it work with my problem. In that model each person is a node and family members modeled as a complete directed graph.
---
### Author:  [@Datseris](https://discourse.julialang.org/u/Datseris)
#### Post date: [May 20, 2024, 11:59am UTC](https://discourse.julialang.org/t/agents-jl-multiagent-methoderror-cannot-convert-an-object-of-type-people-to-an-object-of-type-family/114466/4 "2024-05-20T11:59:06Z")
If I may give a performance advice:
It appears that there is no reason to have `Family` be an agent (i.e., a sub-kind of `@multiagent`) because `Family` is simply a relational structure, not an entity that can move and die.
What I would recommend instead is that you store all Families in a dictionary as a model property. Families then would be a dictionary mapping integer indices to a `Vector{Int}`. The integer indices are just the enumerator of the families (the same as an Agent ID); we use dictionaries in case families may die or be created during the model evolution. The `Vector{Int}` for each family simply stores the agent IDs belonging to that family. It is avector so it can be mutated if family members die.
Each agent has a field `family::Int`, which, as @nivertech said, it is just a pointer to the family they are part of.
So, given an agent, that’s how you get all its family members:
```julia
agent = random_agent(model)
family_id = agent.family_id # this is an integer
family = model.families[family_id] # this is a vector of integers
```
I believe this would bring you drastic perforamnce increase over having a graph structure for the families. But maybe test it as well, because my method would bring some performance _downside_ when _initializing_ the whole model, as some book keeping on the family indices needs to be made! 😃
---
### Author:  [@Tortar](https://discourse.julialang.org/u/Tortar)
#### Post date: [May 20, 2024, 12:31pm UTC](https://discourse.julialang.org/t/agents-jl-multiagent-methoderror-cannot-convert-an-object-of-type-people-to-an-object-of-type-family/114466/5 "2024-05-20T12:31:30Z")
As @nivertech said they are just variants of the same underlying type `People`, for this reason you can instead do:
```julia
julia> using Agents
julia> @multiagent struct People(GraphAgent)
@subagent struct Person
age::Integer
health_condition::Float32
gender::Integer
family::People # here you use People
end
@subagent struct Family
number_of_members::Int
end
end
julia> Person(1,1,32,0.5,1, Family(1,1,5))
Person(1, 1, 32, 0.5, 1, Family(1, 1, 5)::People)::People
```
but as @Datseris points out there can be better ways to express this relationship, hope this helps!
---
### Author:  [@Tortar](https://discourse.julialang.org/u/Tortar)
#### Post date: [May 20, 2024, 12:51pm UTC](https://discourse.julialang.org/t/agents-jl-multiagent-methoderror-cannot-convert-an-object-of-type-people-to-an-object-of-type-family/114466/6 "2024-05-20T12:51:05Z")
maybe this is still confusing so I will add a little more explaination: the `Family` “type” is actually only a constructor for `People` variants/kinds, that is to say that `typeof(Family(1, 1, 5))` is actually `People`, so when you try to use a declaration as `family::Family` you aren’t actually doing what seems to be implied.
At the same time, it could automagically work because we are in a macro context so `family::Family` could be substituted with `family::People` before the final type is evaluated, but this is yet not implemented, but maybe I will try to do it in the future 🙂