# Get list of parameters from Turing model

**URL:** <https://discourse.julialang.org/t/get-list-of-parameters-from-turing-model/66278>\
**Category:** Probabilistic Programming\
**Tags:** turing\
**Created:** [August 12, 2021, 4:27pm UTC](https://discourse.julialang.org/t/get-list-of-parameters-from-turing-model/66278 "2021-08-12T16:27:31Z")\
**Posts on this page:** 17\
**Page:** 1

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**Author:** ![sijo](https://avatars.discourse-cdn.com/v4/letter/s/da6949/32.png) [@sijo](https://discourse.julialang.org/u/sijo)\
**Post date:** [August 12, 2021, 4:27pm UTC](https://discourse.julialang.org/t/get-list-of-parameters-from-turing-model/66278/1 "2021-08-12T16:27:31Z")

</div>

How can I get the list of parameters in a Turing model?

I’m trying to generate programmatically a list of initial values to pass with `init_params`, so I need to know the symbols, in the correct order.

For example, given the following model I’d like to get the tuple `(σ, μ)` :

```julia
@model function mymodel(x)
    σ ~ Exponential()
    μ ~ Normal(2.0, 1.0)
    x .~ Normal(μ, σ)
    
    return μ, σ
end

m = mymodel([1.0, 2.0, 3.0])

ch = sample(m, NUTS(), 1000, discard_adapt=false, init_params=[0.5, 5])

```

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<div class="post-metadata">

**Author:** ![stst](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/stst/32/17252_2.png) [@stst](https://discourse.julialang.org/u/stst)\
**Post date:** [August 16, 2021, 5:36am UTC](https://discourse.julialang.org/t/get-list-of-parameters-from-turing-model/66278/2 "2021-08-16T05:36:04Z")

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I don’t know about a direct way to query the model, but here’s an inefficient way via the `Chains` object returned by `sample`:

```julia
julia> ch = sample(m,Prior(),1); ch.name_map.parameters
2-element Vector{Symbol}:
 :μ
 :σ

```

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<div class="post-metadata">

**Author:** ![cpfiffer](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/cpfiffer/32/208747_2.png) [@cpfiffer](https://discourse.julialang.org/u/cpfiffer)\
**Post date:** [August 16, 2021, 1:56pm UTC](https://discourse.julialang.org/t/get-list-of-parameters-from-turing-model/66278/3 "2021-08-16T13:56:13Z")

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This is probably a good approach for now, though at some point this should be made easier.

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**Author:** ![cscherrer](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/cscherrer/32/7631_2.png) [@cscherrer](https://discourse.julialang.org/u/cscherrer)\
**Post date:** [August 16, 2021, 2:30pm UTC](https://discourse.julialang.org/t/get-list-of-parameters-from-turing-model/66278/4 "2021-08-16T14:30:41Z")

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FWIW in Soss you can do

```julia
julia> mymodel = @model n begin
       σ ~ Exponential()
       μ ~ Normal(2.0, 1.0)
       x ~ Normal(μ,σ) |> iid(n)
       end;

julia> arguments(mymodel)
1-element Vector{Symbol}:
 :n

julia> sampled(mymodel)
3-element Vector{Symbol}:
 :σ
 :μ
 :x 

```

And if you have some observations,

```julia
julia> observed(mymodel() | (x = randn(10),))
(:x,)

```

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<div class="post-metadata">

**Author:** ![sijo](https://avatars.discourse-cdn.com/v4/letter/s/da6949/32.png) [@sijo](https://discourse.julialang.org/u/sijo)\
**Post date:** [August 17, 2021, 7:54am UTC](https://discourse.julialang.org/t/get-list-of-parameters-from-turing-model/66278/5 "2021-08-17T07:54:46Z")

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Thanks for all the answers. Another option I found is `DynamicPPL.syms(DynamicPPL.VarInfo(m))` (but I’m not sure how advisable it is to use these unexported DynamicPPL methods).

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<div class="post-metadata">

**Author:** ![cpfiffer](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/cpfiffer/32/208747_2.png) [@cpfiffer](https://discourse.julialang.org/u/cpfiffer)\
**Post date:** [August 17, 2021, 3:21pm UTC](https://discourse.julialang.org/t/get-list-of-parameters-from-turing-model/66278/6 "2021-08-17T15:21:55Z")

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I think it’s fine – as far as I’m aware those two methods are likely to continue to be around.

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<div class="post-metadata">

**Author:** ![stst](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/stst/32/17252_2.png) [@stst](https://discourse.julialang.org/u/stst)\
**Post date:** [August 18, 2021, 4:39am UTC](https://discourse.julialang.org/t/get-list-of-parameters-from-turing-model/66278/7 "2021-08-18T04:39:46Z")

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Nice, this looks so much less hacky than going through sampling (as I proposed earlier)!

Now, curiously, the two approaches give different parameter orders.

```julia
julia> DynamicPPL.syms(DynamicPPL.VarInfo(m))
(:σ, :μ)

julia> ch = sample(m,Prior(),1); ch.name_map.parameters
2-element Vector{Symbol}:
 :μ
 :σ

```

Which of the two orders is relevant for the parameter initialization in your initial post?

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<div class="post-metadata">

**Author:** ![sijo](https://avatars.discourse-cdn.com/v4/letter/s/da6949/32.png) [@sijo](https://discourse.julialang.org/u/sijo)\
**Post date:** [August 18, 2021, 7:39am UTC](https://discourse.julialang.org/t/get-list-of-parameters-from-turing-model/66278/8 "2021-08-18T07:39:36Z")

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Uhh… good question! It seems to be working as expected with the order from `DynamicPPL.syms(DynamicPPL.VarInfo(m))`. It’s also the order of the data in the chain’s underlying AxisArrays (see `ch.value`).

I wonder what the `ch.name_map.parameters` order is about… Just displaying the chain (`display(ch)`) shows this order in the header, and the other order in the summary stats:

```julia
Chains MCMC chain (1000×14×1 Array{Float64, 3}):

Iterations = 1:1:1000
Number of chains = 1
Samples per chain = 1000
Wall duration = 10.55 seconds
Compute duration = 10.55 seconds
parameters = μ, σ
internals = lp, n_steps, is_accept, acceptance_rate, log_density, hamiltonian_energy, hamiltonian_energy_error, max_hamiltonian_energy_error, tree_depth, numerical_error, step_size, nom_step_size

Summary Statistics
  parameters mean std naive_se mcse ess rhat e ⋯
      Symbol Float64 Float64 Float64 Float64 Float64 Float64 ⋯

           σ 1.1765 0.5388 0.0170 0.0246 411.3738 1.0006 ⋯
           μ 1.9466 0.6001 0.0190 0.0182 295.0682 0.9990 ⋯

```

I had filed a related issue [here](https://github.com/TuringLang/MCMCChains.jl/issues/326) but the most relevant is probably [this one](https://github.com/TuringLang/MCMCChains.jl/issues/311).

---

<div class="post-metadata">

**Author:** ![cpfiffer](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/cpfiffer/32/208747_2.png) [@cpfiffer](https://discourse.julialang.org/u/cpfiffer)\
**Post date:** [August 18, 2021, 4:37pm UTC](https://discourse.julialang.org/t/get-list-of-parameters-from-turing-model/66278/9 "2021-08-18T16:37:22Z")

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The “correct” one if you want to work with `init_params` is `DynamicPPL.syms(DynamicPPL.VarInfo(m))`, since this works very closely with the model block.

`ch.name_map.parameters` is constructed later in `MCMCChains` and isn’t necessarily the best indicator of model parameter order.

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<div class="post-metadata">

**Author:** ![dlakelan](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/dlakelan/32/8491_2.png) [@dlakelan](https://discourse.julialang.org/u/dlakelan)\
**Post date:** [November 21, 2021, 11:30pm UTC](https://discourse.julialang.org/t/get-list-of-parameters-from-turing-model/66278/10 "2021-11-21T23:30:06Z")

</div>

There really needs to be a public API for this. A lot of examples have 1 to 10 parameters, and rely on people entering stuff by hand, but I work with models with 2000 parameters easily (let’s say one parameter for each person in a survey or whatever), and if I want to do initialization or describe a complex Gibbs update (ie. update all the discrete parameters with one kind of update, and some of the continuous parameters with a diffusive update, and others with NUTS) then you need to do stuff programmatically.

Of course, the provided solution works, but it should be documented somewhere and if it’s not intended to be the public API why not create a public API.

For example why not do `params(modelObject)`

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<div class="post-metadata">

**Author:** ![DominiqueMakowski](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/dominiquemakowski/32/51410_2.png) [@DominiqueMakowski](https://discourse.julialang.org/u/DominiqueMakowski)\
**Post date:** [July 10, 2023, 12:57pm UTC](https://discourse.julialang.org/t/get-list-of-parameters-from-turing-model/66278/11 "2023-07-10T12:57:04Z")

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Or `coefnames()` as in R…

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<div class="post-metadata">

**Author:** ![dlakelan](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/dlakelan/32/8491_2.png) [@dlakelan](https://discourse.julialang.org/u/dlakelan)\
**Post date:** [November 14, 2024, 7:29pm UTC](https://discourse.julialang.org/t/get-list-of-parameters-from-turing-model/66278/12 "2024-11-14T19:29:38Z")

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So yeah, years later, is there an “approved” way to get the names of the parameters?

Specifically I’m using a Turing model to construct a custom “tempered model” struct which just uses a LogDensityFunction struct to evaluate the logdensity of the turing model and divides by a given constant temperature. Then I’m slice-sampling this model, and I get a vector of SliceSampling.Transition objects. I want to manually construct a Chains object and I want to know what names I should put for each dimension…

Any updated info?

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<div class="post-metadata">

**Author:** ![opera\_malenky](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/opera_malenky/32/8213_2.png) [@opera\_malenky](https://discourse.julialang.org/u/opera_malenky)\
**Post date:** [November 14, 2024, 7:49pm UTC](https://discourse.julialang.org/t/get-list-of-parameters-from-turing-model/66278/13 "2024-11-14T19:49:05Z")

</div>

It’s been a while since I messed with it, but IIRC there are some methods in the MCMCChains package for getting parameter names from output, e.g., `names(chains::Chains)` or the like.

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<div class="post-metadata">

**Author:** ![dlakelan](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/dlakelan/32/8491_2.png) [@dlakelan](https://discourse.julialang.org/u/dlakelan)\
**Post date:** [November 14, 2024, 7:57pm UTC](https://discourse.julialang.org/t/get-list-of-parameters-from-turing-model/66278/14 "2024-11-14T19:57:43Z")

</div>

yeah, except I’m trying to _construct_ a chain so I don’t have one to look at.

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<div class="post-metadata">

**Author:** ![dlakelan](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/dlakelan/32/8491_2.png) [@dlakelan](https://discourse.julialang.org/u/dlakelan)\
**Post date:** [November 14, 2024, 8:55pm UTC](https://discourse.julialang.org/t/get-list-of-parameters-from-turing-model/66278/15 "2024-11-14T20:55:58Z")

</div>

It is beginning to look like the easiest way for me though is to simply sample a single sample from the underlying Turing model, and then use the names there to construct the chain from the slice sampling transitions

I see that turing does some stuff in \_params\_to\_array inside src/mcmc/inference.jl to get these names, and it’s nontrivial voodoo.

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<div class="post-metadata">

**Author:** ![opera\_malenky](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/opera_malenky/32/8213_2.png) [@opera\_malenky](https://discourse.julialang.org/u/opera_malenky)\
**Post date:** [November 14, 2024, 9:06pm UTC](https://discourse.julialang.org/t/get-list-of-parameters-from-turing-model/66278/16 "2024-11-14T21:06:24Z")

</div>

I don’t know if it preserves the order you want for initialization (it seems to), but you can also call `keys(rand(model))`, which it at least doesn’t have the overhead of constructing the chains object, so it feels less annoying.

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<div class="post-metadata">

**Author:** ![opera\_malenky](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/opera_malenky/32/8213_2.png) [@opera\_malenky](https://discourse.julialang.org/u/opera_malenky)\
**Post date:** [November 14, 2024, 10:50pm UTC](https://discourse.julialang.org/t/get-list-of-parameters-from-turing-model/66278/17 "2024-11-14T22:50:09Z")

</div>

Purely because I was curious myself, and because I sometimes would also like a way to easily extract coefficients _without_ needing to create mock data or actually call `sample`, here’s a horrible hacky (and probably fragile) function that returns the parameters, given a model and a tuple listing the data variables in the model.

It instantiates the model with data as `missing`. A `rand` call creates a `Dict` with keys that tell us all the variables in the model. Then `filter` is used to remove the data variables, leaving only the parameters.

```julia
# 'model' is a Turing model before data has been passed 
# 'data_args' is a tuple of the names of the data 
# (e.g., non-parameter) variables in your model

function parameters(model, data_args)

    # Number of variables that aren't parameters
    n_data_params = length(data_args)

    # Filter out the variables that represent data
    filter(a -> ∉(a, data_args), keys(rand((model)(fill(missing, n_data_params)...))))
end

```