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support negative k for k-subsets #63

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support negative k for k-subsets #63

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8bd03af
subsets: support negative binomial k
stev47 Aug 6, 2019
da7ea91
static subsets: support negative binomial k
stev47 Aug 7, 2019
c43cd24
static binomial: add eltype tests
stev47 Aug 8, 2019
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9 changes: 6 additions & 3 deletions src/IterTools.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -521,7 +521,7 @@ mutable struct BinomialIterState
done::Bool
end

function iterate(it::Binomial, state=BinomialIterState(collect(Int64, 1:it.k), it.k > it.n))
function iterate(it::Binomial, state=BinomialIterState(collect(Int64, 1:it.k), it.k > it.n || it.k < 0))
state.done && return nothing

idx = state.idx
Expand Down Expand Up @@ -556,11 +556,14 @@ end
IteratorSize(::Type{StaticSizeBinomial{K, C}}) where {K, C} = HasLength()
IteratorEltype(::Type{StaticSizeBinomial{K, C}}) where {K, C} = IteratorEltype(C)

eltype(::Type{StaticSizeBinomial{K, C}}) where {K, C} = NTuple{K, eltype(C)}
eltype(::Type{StaticSizeBinomial{K, C}}) where {K, C} = K < 0 ? Union{} : NTuple{K, eltype(C)}
length(it::StaticSizeBinomial{K}) where {K} = binomial(length(it.xs), K)

subsets(xs::C, ::Val{K}) where {K, C} = StaticSizeBinomial{K, C}(xs)

# Special case for K < 0
iterate(it::StaticSizeBinomial{k}) where k = k < 0 ? nothing : _iterate(it)
iterate(it::StaticSizeBinomial{k}, state) where k = k < 0 ? nothing : _iterate(it, state)
# Special case for K == 0
iterate(it::StaticSizeBinomial{0}, state=false) = state ? nothing : ((), true)

Expand All @@ -579,7 +582,7 @@ function advance(it::StaticSizeBinomial{K}, idx) where {K}
end
advance(it::StaticSizeBinomial, idx::NTuple{1}) = (idx[end]+1,)

function iterate(it::StaticSizeBinomial{K}, idx=ntuple(identity, Val{K}())) where K
function _iterate(it::StaticSizeBinomial{K}, idx=ntuple(identity, Val{K}())) where K
idx[end] > length(it.xs) && return nothing
return (map(i -> it.xs[i], idx), advance(it, idx))
end
Expand Down
9 changes: 6 additions & 3 deletions test/runtests.jl
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Expand Up @@ -223,7 +223,7 @@ include("testing_macros.jl")
@test eltype(eltype(sk4)) == Symbol
@test collect(sk4) == Vector{Symbol}[]

@testset for i in 1:5
@testset for i in -1:5
sk5 = subsets(collect(1:4), i)
@test eltype(eltype(sk5)) == Int
@test length(collect(sk5)) == binomial(4, i)
Expand Down Expand Up @@ -264,9 +264,12 @@ include("testing_macros.jl")
@test eltype(eltype(sk5)) == Symbol
@test collect(sk5) == []

@testset for i in 1:6
@testset for i in -1:6
sk5 = subsets(collect(1:4), Val{i}())
@test eltype(eltype(sk5)) == Int
# there is no sensible element type information for i < 1
i < 0 && @test eltype(sk5) == Union{}
i == 0 && @test eltype(sk5) == Tuple{}
i >= 1 && @test eltype(eltype(sk5)) == Int
@test length(collect(sk5)) == binomial(4, i)
end

Expand Down