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Alternate #81

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940177a
Change tab indentation to space indentation
gustaphe Nov 28, 2020
6848eed
Add alternate
gustaphe Nov 28, 2020
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81 changes: 73 additions & 8 deletions src/IterTools.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -30,7 +30,9 @@ export
takewhile,
properties,
propertyvalues,
fieldvalues
fieldvalues,
alternate


function has_length(it)
it_size = IteratorSize(it)
Expand Down Expand Up @@ -590,14 +592,14 @@ iterate(it::StaticSizeBinomial{0}, state=false) = state ? nothing : ((), true)
pop(t::NTuple) = reverse(tail(reverse(t))), t[end]

function advance(it::StaticSizeBinomial{K}, idx) where {K}
xs = it.xs
lidx, i = pop(idx)
xs = it.xs
lidx, i = pop(idx)
i += 1
if i > length(xs) - K + length(idx)
lidx = advance(it, lidx)
i = lidx[end] + 1
end
return (lidx..., i)
if i > length(xs) - K + length(idx)
lidx = advance(it, lidx)
i = lidx[end] + 1
end
return (lidx..., i)
end
advance(it::StaticSizeBinomial, idx::NTuple{1}) = (idx[end]+1,)

Expand Down Expand Up @@ -1031,4 +1033,67 @@ function iterate(fs::FieldValues, state=1)
return (getfield(fs.x, state), state + 1)
end

# Alternate

struct Alternate{Is<:Tuple}
xs::Is
end
"""
alternate(xs...)
Alternates through each of the given iterators in order, shuffling their values
until one of them runs out.

```jldoctest
julia> collect(alternate(1:5,10:-1:1))
1
10
2
9
3
8
4
7
5
6
```
"""
alternate(xs...) = length(xs) == 1 ? xs[1] : Alternate(xs)
function Base.iterate(it::Alternate, state=1)
if state == 1
state=[Array{Any}(nothing,length(it.xs)),1]
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This is not type stable, so will most likely perform poorly. I'd probably do something like

function iterate(it::Interleave, state=(true, iterate(it.a), iterate(it.b)))
    if nothing nonsense
    if state[1]
        state[2][1], (false, iterate(state[2][2], state[3])
    else
        state[3][1], (true, state[2], iterate(state[3][2])
    end
end

end
if isnothing(state[1][state[2]])
itreturn = iterate(it.xs[state[2]])
else
itreturn = iterate(it.xs[state[2]],state[1][state[2]])
end
isnothing(itreturn) && return nothing
state[1][state[2]] = itreturn[2]
state[2] = (state[2] % length(it.xs)) + 1
return (itreturn[1],state)
end
function IteratorEltype(::Type{Alternate{Is}}) where Is
iteratoreltypes = IteratorEltype.(fieldtypes(Is))
any(iteratoreltypes .== Ref(EltypeUnknown())) && return EltypeUnknown()
return HasEltype()
end
eltype(::Type{Alternate{Is}}) where Is = Union{eltype.(fieldtypes(Is))...}
function IteratorSize(::Type{Alternate{Is}}) where Is
iteratorsizes = IteratorSize.(fieldtypes(Is))
any(iteratorsizes .== Ref(SizeUnknown())) && return SizeUnknown()
all(iteratorsizes .== Ref(IsInfinite())) && return IsInfinite()
return HasLength() # Never returns HasShape
end
function length(i::Alternate)
m = Int64(minimum(IteratorSize(x) isa IsInfinite ? Inf : length(x) for x in i.xs))
l = length(i.xs)*m
for x in i.xs
if IteratorSize(x) isa IsInfinite || length(x) > m
l = l+1
else
return l
end
end
end

end # module IterTools
18 changes: 18 additions & 0 deletions test/runtests.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -524,6 +524,24 @@ include("testing_macros.jl")
@test collect(fv3) == Any[]
end

@testset "alternate" begin
intlist1 = 1:5
intlist2 = 2:4:14
inflist = countfrom(1)
unklist = takewhile(x -> x ≤ 10, countfrom(1))
shapedlist = [1 2 3;2 4 6]
str = "String"
@test eltype(alternate(intlist1,intlist2)) == Int64
@test eltype(alternate(intlist1,str)) == Union{Int64,Char}
@test length(alternate(intlist1,intlist2)) == 9
@test length(alternate(intlist2,intlist1)) == 8
@test IteratorSize(alternate(inflist,inflist)) isa IsInfinite
@test IteratorSize(alternate(intlist1,unklist)) isa SizeUnknown
@test IteratorSize(alternate(shapedlist,shapedlist)) isa HasLength
@test alternate(intlist1) == intlist1
@test collect(alternate(intlist1,intlist2,inflist)) == [1,2,1,2,6,2,3,10,3,4,14,4,5]
end

@testset "traits overriding defaults" begin
iters = [
firstrest(1:10),
Expand Down