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Fix sampling with UnitWeights #963

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Fix sampling with UnitWeights #963

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29 changes: 24 additions & 5 deletions src/sampling.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -603,6 +603,9 @@ sample(wv::AbstractWeights) = sample(default_rng(), wv)
sample(rng::AbstractRNG, a::AbstractArray, wv::AbstractWeights) = a[sample(rng, wv)]
sample(a::AbstractArray, wv::AbstractWeights) = sample(default_rng(), a, wv)

# Specialization for `UnitWeights`
sample(rng::AbstractRNG, wv::UnitWeights) = rand(rng, 1:length(wv))

"""
direct_sample!([rng], a::AbstractArray, wv::AbstractWeights, x::AbstractArray)

Expand Down Expand Up @@ -633,6 +636,14 @@ end
direct_sample!(a::AbstractArray, wv::AbstractWeights, x::AbstractArray) =
direct_sample!(default_rng(), a, wv, x)

# Specialization for `UnitWeights`
function direct_sample!(rng::AbstractRNG, a::AbstractArray, wv::UnitWeights, x::AbstractArray)
if length(a) != length(wv)
throw(DimensionMismatch(lazy"Number of samples ($(length(a))) and sample weights ($(length(wv))) must be equal."))
end
return direct_sample!(rng, a, x)
end

"""
alias_sample!([rng], a::AbstractArray, wv::AbstractWeights, x::AbstractArray)

Expand Down Expand Up @@ -741,7 +752,7 @@ function efraimidis_a_wsample_norep!(rng::AbstractRNG, a::AbstractArray,
# calculate keys for all items
keys = randexp(rng, n)
for i in 1:n
@inbounds keys[i] = wv.values[i]/keys[i]
@inbounds keys[i] = wv[i]/keys[i]
end

# return items with largest keys
Expand Down Expand Up @@ -787,7 +798,7 @@ function efraimidis_ares_wsample_norep!(rng::AbstractRNG, a::AbstractArray,
s = 0
@inbounds for _s in 1:n
s = _s
w = wv.values[s]
w = wv[s]
w < 0 && error("Negative weight found in weight vector at index $s")
if w > 0
i += 1
Expand All @@ -802,7 +813,7 @@ function efraimidis_ares_wsample_norep!(rng::AbstractRNG, a::AbstractArray,
@inbounds threshold = pq[1].first

@inbounds for i in s+1:n
w = wv.values[i]
w = wv[i]
w < 0 && error("Negative weight found in weight vector at index $i")
w > 0 || continue
key = w/randexp(rng)
Expand Down Expand Up @@ -861,7 +872,7 @@ function efraimidis_aexpj_wsample_norep!(rng::AbstractRNG, a::AbstractArray,
s = 0
@inbounds for _s in 1:n
s = _s
w = wv.values[s]
w = wv[s]
w < 0 && error("Negative weight found in weight vector at index $s")
if w > 0
i += 1
Expand All @@ -877,7 +888,7 @@ function efraimidis_aexpj_wsample_norep!(rng::AbstractRNG, a::AbstractArray,
X = threshold*randexp(rng)

@inbounds for i in s+1:n
w = wv.values[i]
w = wv[i]
w < 0 && error("Negative weight found in weight vector at index $i")
w > 0 || continue
X -= w
Expand Down Expand Up @@ -958,6 +969,14 @@ sample(a::AbstractArray, wv::AbstractWeights, dims::Dims;
replace::Bool=true, ordered::Bool=false) =
sample(default_rng(), a, wv, dims; replace=replace, ordered=ordered)

# Specialization for `UnitWeights`
function sample!(rng::AbstractRNG, a::AbstractArray, wv::UnitWeights, x::AbstractArray; replace::Bool=true, ordered::Bool=false)
if length(a) != length(wv)
throw(DimensionMismatch(lazy"Number of samples ($(length(a))) and sample weights ($(length(wv))) must be equal."))
end
return sample!(rng, a, x; replace, ordered)
end

# wsample interface

"""
Expand Down
48 changes: 48 additions & 0 deletions test/sampling.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -297,3 +297,51 @@ end
end
end
end

# Custom unit weights without `values` field
struct YAUnitWeights <: StatsBase.AbstractWeights{Int, Int, Vector{Int}}
n::Int
end
Base.sum(wv::YAUnitWeights) = wv.n
Base.length(wv::YAUnitWeights) = wv.n
Base.isempty(wv::YAUnitWeights) = iszero(wv.n)
Base.size(wv::YAUnitWeights) = (wv.n,)
Base.axes(wv::YAUnitWeights) = (Base.OneTo(wv.n),)
function Base.getindex(wv::YAUnitWeights, i::Int)
@boundscheck checkbounds(wv, i)
return 1
end

@testset "issue #950" begin
# Sampling with unit weights behaves the same as sampling without weights
Random.seed!(123)
xs = sample(1:100, uweights(100), 10; replace=false)
Random.seed!(123)
@test xs == sample(1:100, 10; replace=false)

Random.seed!(123)
x = sample(uweights(100))
Random.seed!(123)
@test x == sample(1:100)

Random.seed!(123)
xs = direct_sample!(1:100, uweights(100), Vector{Int}(undef, 10))
Random.seed!(123)
@test xs == direct_sample!(1:100, Vector{Int}(undef, 10))

# Errors
@test_throws DimensionMismatch("Number of samples (100) and sample weights (99) must be equal.") sample(1:100, uweights(99), 10; replace=false)
@test_throws DimensionMismatch("Number of samples (80) and sample weights (53) must be equal.") direct_sample!(1:80, uweights(53), Vector{Int}(undef, 10))

# Custom units don't error and behave the same as sampling with `Weights`
Random.seed!(123)
xs = sample(1:100, YAUnitWeights(100), 10; replace=false)
Random.seed!(123)
@test xs == sample(1:100, weights(ones(Int, 100)), 10; replace=false)
for f in (StatsBase.efraimidis_a_wsample_norep!, StatsBase.efraimidis_ares_wsample_norep!, StatsBase.efraimidis_aexpj_wsample_norep!)
Random.seed!(123)
xs = f(1:100, YAUnitWeights(100), Vector{Int}(undef, 10))
Random.seed!(123)
@test xs == f(1:100, weights(ones(Int, 100)), Vector{Int}(undef, 10))
end
end
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