Add Base.get method for ModeResult (#2269)

* Add Base.get method for ModeResult

* Make get(::ModeResult, itr) work for any iterator

* Fix array type in get(::ModeResult, ...)

src/optimisation/Optimisation.jl

@@ -273,6 +273,37 @@ StatsBase.params(m::ModeResult) = StatsBase.coefnames(m)
 StatsBase.vcov(m::ModeResult) = inv(StatsBase.informationmatrix(m))
 StatsBase.loglikelihood(m::ModeResult) = m.lp
 
+"""
+    Base.get(m::ModeResult, var_symbol::Symbol)
+    Base.get(m::ModeResult, var_symbols)
+
+Return the values of all the variables with the symbol(s) `var_symbol` in the mode result
+`m`. The return value is a `NamedTuple` with `var_symbols` as the key(s). The second
+argument should be either a `Symbol` or an iterator of `Symbol`s.
+"""
+function Base.get(m::ModeResult, var_symbols)
+    log_density = m.f
+    # Get all the variable names in the model. This is the same as the list of keys in
+    # m.values, but they are more convenient to filter when they are VarNames rather than
+    # Symbols.
+    varnames = collect(
+        map(first, Turing.Inference.getparams(log_density.model, log_density.varinfo))
+    )
+    # For each symbol s in var_symbols, pick all the values from m.values for which the
+    # variable name has that symbol.
+    et = eltype(m.values)
+    value_vectors = Vector{et}[]
+    for s in var_symbols
+        push!(
+            value_vectors,
+            [m.values[Symbol(vn)] for vn in varnames if DynamicPPL.getsym(vn) == s],
+        )
+    end
+    return (; zip(var_symbols, value_vectors)...)
+end
+
+Base.get(m::ModeResult, var_symbol::Symbol) = get(m, (var_symbol,))
+
 """
     ModeResult(log_density::OptimLogDensity, solution::SciMLBase.OptimizationSolution)
 

test/optimisation/Optimisation.jl

@@ -4,13 +4,14 @@ using ..Models: gdemo, gdemo_default
 using Distributions
 using Distributions.FillArrays: Zeros
 using DynamicPPL: DynamicPPL
-using LinearAlgebra: I
+using LinearAlgebra: Diagonal, I
 using Random: Random
 using Optimization
 using Optimization: Optimization
 using OptimizationBBO: OptimizationBBO
 using OptimizationNLopt: OptimizationNLopt
 using OptimizationOptimJL: OptimizationOptimJL
+using ReverseDiff: ReverseDiff
 using StatsBase: StatsBase
 using StatsBase: coef, coefnames, coeftable, informationmatrix, stderror, vcov
 using Test: @test, @testset, @test_throws
@@ -591,6 +592,30 @@ using Turing
         @test result.values[:x] ≈ 0 atol = 1e-1
         @test result.values[:y] ≈ 100 atol = 1e-1
     end
+
+    @testset "get ModeResult" begin
+        @model function demo_model(N)
+            half_N = N ÷ 2
+            a ~ arraydist(LogNormal.(fill(0, half_N), 1))
+            b ~ arraydist(LogNormal.(fill(0, N - half_N), 1))
+            covariance_matrix = Diagonal(vcat(a, b))
+            x ~ MvNormal(covariance_matrix)
+            return nothing
+        end
+
+        N = 12
+        m = demo_model(N) | (x=randn(N),)
+        result = maximum_a_posteriori(m)
+        get_a = get(result, :a)
+        get_b = get(result, :b)
+        get_ab = get(result, [:a, :b])
+        @assert keys(get_a) == (:a,)
+        @assert keys(get_b) == (:b,)
+        @assert keys(get_ab) == (:a, :b)
+        @assert get_b[:b] == get_ab[:b]
+        @assert vcat(get_a[:a], get_b[:b]) == result.values.array
+        @assert get(result, :c) == (; :c => Array{Float64}[])
+    end
 end
 
 end