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add method for getindex(::ProductIterator, inds...) #49965

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add method for getindex(::ProductIterator, inds...) #49965

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d84bc95
add getindex method to ProductIterator
MasonProtter May 26, 2023
8cc6157
Merge branch 'master' into patch-9
MasonProtter Nov 26, 2023
bbc374f
use `Base.map`
MasonProtter Nov 26, 2023
af4e77a
Update iterators.jl
MasonProtter Nov 26, 2023
dced4c2
add some tests
MasonProtter Nov 26, 2023
b59e86b
whitespace
MasonProtter Nov 26, 2023
abb88d5
Merge branch 'master' into patch-9
MasonProtter Dec 6, 2023
0c089e5
fixup
MasonProtter Dec 6, 2023
5493114
Update iterators.jl
MasonProtter Dec 6, 2023
e7b6aa2
Merge branch 'master' into patch-9
MasonProtter Dec 9, 2023
2d9d083
Merge branch 'master' into patch-9
MasonProtter Nov 19, 2024
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1 change: 1 addition & 0 deletions base/iterators.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -1128,6 +1128,7 @@ end
reverse(p::ProductIterator) = ProductIterator(Base.map(reverse, p.iterators))
last(p::ProductIterator) = Base.map(last, p.iterators)
intersect(a::ProductIterator, b::ProductIterator) = ProductIterator(intersect.(a.iterators, b.iterators))
getindex(p::ProductIterator, inds...) = map(getindex, p.iterators, inds)
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@FelixBenning FelixBenning Jun 1, 2023 •
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So here is an actual problem with this implementation:

julia> a = Iterators.product([1 2; 3 4], 1:2);

julia> b = collect(a)
2×2×2 Array{Tuple{Int64, Int64}, 3}:
[:, :, 1] =
 (1, 1)  (2, 1)
 (3, 1)  (4, 1)

[:, :, 2] =
 (1, 2)  (2, 2)
 (3, 2)  (4, 2)

julia> b[1,1,1]
(1, 1)

julia> map(getindex, a.iterators, (1,1,1))
ERROR: BoundsError: attempt to access Tuple{} at index [1]
Stacktrace:
 [1] getindex(t::Tuple, i::Int64)
   @ Base ./tuple.jl:29
 [2] map (repeats 3 times)
   @ ./tuple.jl:250 [inlined]
 [3] top-level scope
   @ REPL[24]:1

i.e. map assumes every iterator is one dimensional. The following should be a fix I think

function getindex(prod::ProductIterator, indices...)
    return _prod_getindex(prod.iterators, indices...)
end
_prod_getindex(::Tuple{}) = ()
function _prod_getindex(p_vecs::Tuple, indices...)
    v = first(p_vecs)
    n = ndims(v)
    return (
        v[indices[1:n]...],
        _prod_getindex(Base.tail(p_vecs), indices[n+1:end]...)...
    )
end

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you also need to manage all types of access variants (colons, ranges, ...) if you don't limit indices to Vararg{Int,N}. But for this you need to determine N (i.e. ndims) statically.


# flatten an iterator of iterators

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