# How to obtain val.argument of KeySet of OrderCollection?
**URL:** https://discourse.julialang.org/t/how-to-obtain-val-argument-of-keyset-of-ordercollection/123547
**Category:** General Usage
**Tags:** question
**Created:** [December 6, 2024, 4:58pm UTC](https://discourse.julialang.org/t/how-to-obtain-val-argument-of-keyset-of-ordercollection/123547 "2024-12-06T16:58:15Z")
**Posts on this page:** 5
**Page:** 1
### Author:  [@Domenico\_Lahaye](https://discourse.julialang.org/u/Domenico_Lahaye)
#### Post date: [December 6, 2024, 4:58pm UTC](https://discourse.julialang.org/t/how-to-obtain-val-argument-of-keyset-of-ordercollection/123547/1 "2024-12-06T16:58:16Z")
Assume given
```julia
flatten(a) = collect(Iterators.flatten(a))
```
Assume furthermore given
```julia
julia> diff_eom.equations
OrderedCollections.OrderedDict{Symbolics.Num, Symbolics.Equation} with 1 entry:
x(t) => Differential(t)(Differential(t)(x(t))) - F*cos(t*ω) + x(t)*(ω0^2) ~ 0
```
Then the following two functions work beautifully and as a charm (stolen from HarmonicBalance.jl)
```julia
julia> keys(diff_eom.equations)
KeySet for a OrderedCollections.OrderedDict{Symbolics.Num, Symbolics.Equation} with 1 entry. Keys:
x(t)
```
and
```julia
julia> flatten(unique([x.val.arguments for x in keys(diff_eom.equations)]))
1-element Vector{Any}:
t
```
Assume wishing to extend this to (and later to N \>\> 1 ODEs)
```julia
julia> diff_eq
System of 2 differential equations
Variables: (x(t))[1], (x(t))[2]
Harmonic ansatz: (x(t))[1] => ; (x(t))[2] => ;
Differential(t)(Differential(t)((x(t))[1])) - k*(x(t))[2] + (x(t))[1]*(ω0^2) ~ F*cos(t*ω)
Differential(t)(Differential(t)((x(t))[2])) - k*(x(t))[1] + (x(t))[2]*(ω0^2) ~ 0
```
Then the keys become
```julia
julia> keys(diff_eq.equations)
KeySet for a OrderedCollections.OrderedDict{Symbolics.Num, Symbolics.Equation} with 2 entries. Keys:
(x(t))[1]
(x(t))[2]
```
How do I get the t out in this case?
Merely repeating above is insufficient as shown below (Vector{Any} is no good sign)
```julia
julia> flatten(unique([x.val.arguments for x in keys(diff_eq.equations)]))
4-element Vector{Any}:
x(t)
1
x(t)
2
```
What is an appropriate syntax here? Thanks.
---
### Author:  [@Domenico\_Lahaye](https://discourse.julialang.org/u/Domenico_Lahaye)
#### Post date: [December 6, 2024, 10:05pm UTC](https://discourse.julialang.org/t/how-to-obtain-val-argument-of-keyset-of-ordercollection/123547/2 "2024-12-06T22:05:11Z")
Part of the issue is a syntax issues.
For the scalar case, this works
```julia
julia> @variables t, s(t)
2-element Vector{Symbolics.Num}:
t
s(t)
julia> s.val.arguments
1-element Vector{Any}:
t
```
How do I make this work for the vector-valued case? How do I extract t from
```julia
julia> @variables t, (v(t))[1:2]
2-element Vector{Any}:
t
(v(t))[1:2]
```
Below does not work yet.
```julia
julia> v[1].val.arguments
2-element Vector{Any}:
v(t)
1
```
Thanks.
---
### Author:  [@abraemer](https://discourse.julialang.org/u/abraemer)
#### Post date: [December 7, 2024, 6:15am UTC](https://discourse.julialang.org/t/how-to-obtain-val-argument-of-keyset-of-ordercollection/123547/3 "2024-12-07T06:15:37Z")
Try (using your last example):
`v[1].val.arguments[1].val.arguments`
---
### Author:  [@Domenico\_Lahaye](https://discourse.julialang.org/u/Domenico_Lahaye)
#### Post date: [December 7, 2024, 6:40am UTC](https://discourse.julialang.org/t/how-to-obtain-val-argument-of-keyset-of-ordercollection/123547/4 "2024-12-07T06:40:36Z")
```julia
julia> v
(v(t))[1:2]
julia> v[1].val.arguments[1].val.arguments
ERROR: type Term has no field val.
Stacktrace:
[1] error(s::String)
@ Base ./error.jl:35
[2] throw_no_field(::Val{:Term}, s::Symbol)
@ Unityper ~/.julia/packages/Unityper/BiodR/src/compactify.jl:505
[3] getproperty(x::SymbolicUtils.BasicSymbolic{Vector{Real}}, s::Symbol)
@ SymbolicUtils ~/.julia/packages/Unityper/BiodR/src/compactify.jl:310
[4] top-level scope
@ REPL[82]:1
```
---
### Author:  [@DanielVandH](https://discourse.julialang.org/u/DanielVandH)
#### Post date: [December 7, 2024, 7:03am UTC](https://discourse.julialang.org/t/how-to-obtain-val-argument-of-keyset-of-ordercollection/123547/5 "2024-12-07T07:03:17Z")
```julia
julia> v
(v(t))[1:2]
julia> Symbolics.value(v)
v(t)
julia> arguments(Symbolics.value(v))
1-element Vector{Any}:
t
julia> only(arguments(Symbolics.value(v)))
t
```
```julia
julia> zt
3-element Vector{Num}:
(z(t))[1]
(z(t))[2]
(z(t))[3]
julia> only(arguments(arguments(Symbolics.value(zt[1]))[1]))
t
```
I don’t use Symbolics.jl but there’s probably a better way than this, but it works. You could define a function `get_farg` (or whatever) and use multiple dispatch to give convenient methods for the different forms of your symbolic variables