# Retrieve all variables appearing in a symbolic expression
**URL:** https://discourse.julialang.org/t/retrieve-all-variables-appearing-in-a-symbolic-expression/123846
**Category:** General Usage
**Created:** [December 14, 2024, 10:20pm UTC](https://discourse.julialang.org/t/retrieve-all-variables-appearing-in-a-symbolic-expression/123846 "2024-12-14T22:20:35Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@elvispy](https://discourse.julialang.org/u/elvispy)
#### Post date: [December 14, 2024, 10:20pm UTC](https://discourse.julialang.org/t/retrieve-all-variables-appearing-in-a-symbolic-expression/123846/1 "2024-12-14T22:20:35Z")
I would like to get all the variables involved in an expression, even the implicit ones. For example, if you do
```julia
using Symbolics
@variables x y u(x, y)
println(Symbolics.get_variables(u))
```
You get `1-element Vector{SymbolicUtils.BasicSymbolic}: u(x, y)`. However, i would like to get as a result a 3-element Vector with `u, x` and `y`.
Is there a way to retreive all variables involved in u? (namely, also x and y)
Thanks!
---
### Author:  [@Fe-r-oz](https://discourse.julialang.org/u/Fe-r-oz)
#### Post date: [December 15, 2024, 5:10pm UTC](https://discourse.julialang.org/t/retrieve-all-variables-appearing-in-a-symbolic-expression/123846/2 "2024-12-15T17:10:37Z")
> [@elvispy](#):
>
> Is there a way to retreive all variables involved in u? (namely, also x and y)
To extract all variables from a symbolic expression, including implicit ones, you may want to use the recursive approach:
1. Start by using `get_variables` to get the top-level variables (e.g., `u(x, y)`).
2. Extract the “ops” (e.g., `u`) with `operation` and its “args” (e.g., `x` and `y`) with `arguments`.
3. Recursively apply this process to both the ops and its args to collect all the components.
```julia
using Symbolics
using Symbolics: get_variables, isterm, operation, arguments
function all_vars(expr)
vars = get_variables(expr)
res = Set(vars)
for v in vars
if isterm(v)
res = union(res, all_vars(operation(v)))
for arg in arguments(v)
res = union(res, all_vars(arg))
end
end
end
return res
end
```
```julia
julia> @variables x, y, u(x, y);
julia> all_vars(u)
Set{Any} with 4 elements:
u
u(x, y)
y
x
```
---
### Author:  [@elvispy](https://discourse.julialang.org/u/elvispy)
#### Post date: [December 15, 2024, 5:35pm UTC](https://discourse.julialang.org/t/retrieve-all-variables-appearing-in-a-symbolic-expression/123846/3 "2024-12-15T17:35:52Z")
Nice, thanks!