# Add agent to random position in 3D GridSpace

**URL:** <https://discourse.julialang.org/t/add-agent-to-random-position-in-3d-gridspace/92847>\
**Category:** Modelling & Simulations\
**Tags:** agents\
**Created:** [January 12, 2023, 5:11am UTC](https://discourse.julialang.org/t/add-agent-to-random-position-in-3d-gridspace/92847 "2023-01-12T05:11:42Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![sea\_slug](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/sea_slug/32/52907_2.png) [@sea\_slug](https://discourse.julialang.org/u/sea_slug)\
**Post date:** [January 12, 2023, 5:11am UTC](https://discourse.julialang.org/t/add-agent-to-random-position-in-3d-gridspace/92847/1 "2023-01-12T05:11:43Z")

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I am trying to create a 3D ABM using agents.jl. I am stuck with a very simple issue, I cannot add agents to the GridSpace. I just want to give each agent a random starting point in 3D space.

I have cannibalised the wolf-sheep and the 3D Mixed-Agent Ecosystem with Pathfinding example models, to cerate a reproducible example, the below code works if `dim = (20,20)`, but not if `dim = (20,20,20)`.

I initially tried adding an agent simply using `add_agent!()` but I couldn’t get that to work, so following the 3D Mixed-Agent Ecosystem with Pathfinding example I used the `AStar()` pathfinding function used to add hawks (seems unnecessary since I just want a random starting position and nowhere is restricted space), but that didn’t work either. I keep getting the error message:

```julia
ERROR: MethodError: Cannot `convert` an object of type 
  Tuple{Int64{},Int64{},Int64} to an object of type
  Tuple{Int64{},Int64{}}

```

The error occurs in the `# Add agents` block of code. Any advice would be great!

Reproduceable example:

```julia
using Agents, Agents.Pathfinding
using Random
using InteractiveDynamics
using GLMakie

# sheep agents with no traits (other than id and pos)
@agent Sheep GridAgent{2} begin
end

function initialize_model(;
    n_sheep = 10,
    dims = (20, 20, 20),
    seed = 23182,
)

rng = MersenneTwister(seed)
space = GridSpace(dims, periodic = false)

# define where "sheep" can walk - everywhere
# land_walkmap = BitArray(trues(dims...))

# model properties
properties = (
    landfinder = AStar(space; diagonal_movement = true),
    #landfinder = AStar(space; walkmap = land_walkmap),
    #landfinder = AStar(space; walkmap = land_walkmap, cost_metric = MaxDistance{3}(), diagonal_movement = true),
    fully_grown = falses(dims),
)

model = ABM(Sheep, space; properties, rng, scheduler = Schedulers.randomly, warn = false
)
# Add agents
for _ in 1:n_sheep
    add_agent_pos!(
        Sheep(
            nextid(model), 
            random_walkable(model, model.landfinder),
        ),
        model,
    )
end

# Add grass with random initial growth
for p in positions(model)
    fully_grown = rand(model.rng, Bool)
    model.fully_grown[p...] = fully_grown
end

return model

end

# sheep movement - random
function sheepwolf_step!(sheep::Sheep, model)
    walk!(sheep, rand, model)
end

# grass - something mundane 
function grass_step!(model)
    for p in positions(model)
                model.fully_grown[p...] = true
            end
end

# set up model - fails
sheepwolfgrass = initialize_model() 

```

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<div class="post-metadata">

**Author:** ![fbanning](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/fbanning/32/14972_2.png) [@fbanning](https://discourse.julialang.org/u/fbanning)\
**Post date:** [January 12, 2023, 2:59pm UTC](https://discourse.julialang.org/t/add-agent-to-random-position-in-3d-gridspace/92847/2 "2023-01-12T14:59:26Z")

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There’s a 3D GridSpace model example for the Schelling model in the InteractiveDynamics repository. Maybe this helps you to find out what you want to do?

> <https://github.com/JuliaDynamics/InteractiveDynamics.jl/blob/main/examples/agents/agents_schelling3d.jl>

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<div class="post-metadata">

**Author:** ![Dan](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/dan/32/42581_2.png) [@Dan](https://discourse.julialang.org/u/Dan)\
**Post date:** [January 12, 2023, 3:33pm UTC](https://discourse.julialang.org/t/add-agent-to-random-position-in-3d-gridspace/92847/3 "2023-01-12T15:33:37Z")

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> [@sea\_slug](#):
>
> ```julia
> @agent Sheep GridAgent{2} begin
> end
> 
> ```

That `{2}` looks like it would need to be `{3}`?

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<div class="post-metadata">

**Author:** ![sea\_slug](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/sea_slug/32/52907_2.png) [@sea\_slug](https://discourse.julialang.org/u/sea_slug)\
**Post date:** [January 12, 2023, 7:37pm UTC](https://discourse.julialang.org/t/add-agent-to-random-position-in-3d-gridspace/92847/5 "2023-01-12T19:37:58Z")

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> [@Dan](#):
>
> That `{2}` looks like it would need to be `{3}`?

I’m an idiot. … thank you!

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<div class="post-metadata">

**Author:** ![fbanning](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/fbanning/32/14972_2.png) [@fbanning](https://discourse.julialang.org/u/fbanning)\
**Post date:** [January 17, 2023, 12:47pm UTC](https://discourse.julialang.org/t/add-agent-to-random-position-in-3d-gridspace/92847/6 "2023-01-17T12:47:24Z")

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Great catch, it’s these little things. 🙂