# Error creating a Dict with symbols as indices
**URL:** https://discourse.julialang.org/t/error-creating-a-dict-with-symbols-as-indices/109367
**Category:** New to Julia
**Created:** [January 28, 2024, 8:13pm UTC](https://discourse.julialang.org/t/error-creating-a-dict-with-symbols-as-indices/109367 "2024-01-28T20:13:22Z")
**Posts on this page:** 5
**Page:** 1
### Author:  [@orebas](https://discourse.julialang.org/u/orebas)
#### Post date: [January 28, 2024, 8:13pm UTC](https://discourse.julialang.org/t/error-creating-a-dict-with-symbols-as-indices/109367/1 "2024-01-28T20:13:22Z")
I am trying to emulate some code I have been given, which returns a Dict that has model states from a ModelingToolkit model as indices. But the below code gives an error. Here’s the MWE:
```julia
using ModelingToolkit
function main()
@parameters a
@variables t x1(t)
D = Differential(t)
states = [x1]
parameters = [a]
@named model = ODESystem([
D(x1) ~ a * x1,
], t, states, parameters)
state_vec = ModelingToolkit.states(model)
state_dict = Dict[]
state_dict[state_vec[1]] = "test"
end
main()
```
and here is the error:
```julia
ERROR: LoadError: ArgumentError: invalid index: x1(t) of type SymbolicUtils.BasicSymbolic{Real}
Stacktrace:
[1] to_index(i::SymbolicUtils.BasicSymbolic{Real})
@ Base ./indices.jl:300
[2] to_index(A::Vector{Dict}, i::SymbolicUtils.BasicSymbolic{Real})
@ Base ./indices.jl:277
[3] _to_indices1(A::Vector{Dict}, inds::Tuple{Base.OneTo{Int64}}, I1::SymbolicUtils.BasicSymbolic{Real})
@ Base ./indices.jl:359
[4] to_indices
@ Base ./indices.jl:354 [inlined]
[5] to_indices
@ Base ./indices.jl:345 [inlined]
[6] setindex!(A::Vector{Dict}, v::String, I::SymbolicUtils.BasicSymbolic{Real})
@ Base ./abstractarray.jl:1393
[7] main()
@ Main ~/learning/ODETests/error.jl:16
[8] top-level scope
@ ~/learning/ODETests/error.jl:18
[9] include(fname::String)
@ Base.MainInclude ./client.jl:489
[10] top-level scope
@ REPL[1]:1
in expression starting at /home/orebas/learning/ODETests/error.jl:18
```
---
### Author:  [@oheil](https://discourse.julialang.org/u/oheil)
#### Post date: [January 28, 2024, 8:27pm UTC](https://discourse.julialang.org/t/error-creating-a-dict-with-symbols-as-indices/109367/2 "2024-01-28T20:27:30Z")
```julia
state_dict = Dict[]
```
This is a `Vector{Dict}`.
What you want is:
```julia
julia> state_dict = Dict()
Dict{Any, Any}()
```
Or you give the types, e.g.:
```julia
julia> state_dict = Dict{SymbolicUtils.BasicSymbolic{Real},String}()
```
Can’t test this right now, but perhaps you get what I mean and find the proper type.
---
### Author:  [@orebas](https://discourse.julialang.org/u/orebas)
#### Post date: [January 28, 2024, 8:36pm UTC](https://discourse.julialang.org/t/error-creating-a-dict-with-symbols-as-indices/109367/3 "2024-01-28T20:36:23Z")
Thank you, this solved my problem.
---
### Author:  [@GHTaarn](https://discourse.julialang.org/u/GHTaarn)
#### Post date: [January 28, 2024, 8:45pm UTC](https://discourse.julialang.org/t/error-creating-a-dict-with-symbols-as-indices/109367/4 "2024-01-28T20:45:14Z")
> [@oheil](#):
>
> ```julia-auto
> julia> state_dict = Dict{SymbolicUtils.BasicSymbolic{Real},String}()
>
> ```
A slightly shorter version:
```julia-auto
state_dict = Dict{typeof(state_vec[]),String}()
```
---
### Author:  [@sijo](https://discourse.julialang.org/u/sijo)
#### Post date: [January 29, 2024, 10:02am UTC](https://discourse.julialang.org/t/error-creating-a-dict-with-symbols-as-indices/109367/5 "2024-01-29T10:02:59Z")
Or even shorter and clearer 🙂
```julia
Dict{eltype(state_vec),String}()
```