Names of unknowns have a (t) appendix but DataFrame column names not

[david-hofmann]

A nice to have: consistency between unknown names and DataFrame column names

The names of unknowns/variables of an ODESystem come with a (t) appendix. However, when transforming the solution to a DataFrame the (t) is gone. This way one cannot directly use the name of a variable as an index.
It would be helpful to make naming consistent.

Minimal Reproducible Example 👇

using ModelingToolkit
using DataFrames
using OrdinaryDiffEq

const t = ModelingToolkit.t_nounits
const D = ModelingToolkit.D_nounits

@variables x(t)=1.0
eqn = [D(x) ~ 0.0]

@named sys = ODESystem(eqn,t,[x],[],tspan=(0, 10.0))
sys = structural_simplify(sys)
prob = ODEProblem(sys)
sol = solve(prob)

dfsys = DataFrame(sol)

String(Symbol(unknowns(sys)[1]))
names(dfsys)[2]

Package Versions

Status `~/.julia/environments/v1.10/Project.toml`
  [13f3f980] CairoMakie v0.12.11
⌃ [a93c6f00] DataFrames v1.6.1
⌃ [0c46a032] DifferentialEquations v7.13.0
  [86223c79] Graphs v1.11.2
  [23992714] MAT v0.10.7
⌃ [961ee093] ModelingToolkit v9.40.0
  [769b91e5] Neuroblox v0.4.2 `../../../Projects/neuroblox/codes/Neuroblox.jl`
  [bac558e1] OrderedCollections v1.6.3
⌃ [1dea7af3] OrdinaryDiffEq v6.87.0
⌃ [91a5bcdd] Plots v1.40.1
⌃ [c3e4b0f8] Pluto v0.19.45

Thank you!

[ChrisRackauckas]

@AayushSabharwal I don't think this change is intended right?

@david-hofmann workflow wise, what's the reason for preferring one over the other?

[david-hofmann]

From my (code's) perspective both are equivalent. I can adapt the code either way, it should just be consistent.

[AayushSabharwal]

This hasn't changed in like 9 months since SII 0.3 came out 😅 but it is an inconsistency, since if you convert a DiffEqArray to a DataFrame it'll add the (t) but solutions won't because we have the Tables.jl interface implemented twice for some reason. I'll remove one and/or fix the other depending on which version we want to keep.

[david-hofmann]

I'd appreciate to have everything with the (t) appendix if there is no reason not to have that. No particular reason, just a preference.