add the iteratenz API

src/abstractsparse.jl

@@ -124,4 +124,12 @@ julia> findnz(A)
 """
 function findnz end
 
+"""
+    iternz(A::AbstractSparseArray)
+
+Equivalent to `zip(findnz(A)...)` but does not allocated
+```
+"""
+function iternz end
+
 widelength(x::AbstractSparseArray) = prod(Int64.(size(x)))

src/sparsematrix.jl

@@ -1700,6 +1700,37 @@ function sparse_sortedlinearindices!(I::Vector{Ti}, V::Vector, m::Int, n::Int) w
     return SparseMatrixCSC(m, n, colptr, I, V)
 end
 
+
+abstract type SparseIndexIterate end
+@inline getcolptr(x::SparseIndexIterate) = getcolptr(x.m)
+@inline getrowval(x::SparseIndexIterate) = getrowval(x.m)
+@inline getnzval(x::SparseIndexIterate) = getnzval(x.m)
+@inline nonzeroinds(x::SparseIndexIterate) = nonzeroinds(x.m)
+@inline nonzeros(x::SparseIndexIterate) = nonzeros(x.m)
+@inline nnz(x::SparseIndexIterate) = nnz(x.m)
+
+Base.length(x::SparseIndexIterate) = nnz(x.m)
+Base.size(x::SparseIndexIterate) = size(x.m)
+Base.size(x::SparseIndexIterate, i) = size(x.m)[i]
+struct IterateNZCSC{T<: AbstractSparseMatrixCSC} <: SparseIndexIterate
+    m::T
+end
+
+Base.eltype(::IterateNZCSC{T}) where {Ti, Tv, T <: AbstractSparseMatrixCSC{Tv, Ti}} = Tuple{Ti, Ti, Tv}
+Base.iterate(x::IterateNZCSC, state=(1, 0)) = @inbounds let (j, ind) = state
+    ind += 1
+    while (j < size(x, 2)) && (ind > getcolptr(x)[j + 1] - 1)
+        j += 1
+    end
+    (j > size(x, 2) || ind > getcolptr(x)[end] - 1) && return nothing
+
+    (getrowval(x)[ind], j, getnzval(x)[ind]), (j, ind)
+end
+
+iternz(S::AbstractSparseMatrixCSC) = IterateNZCSC(S)
+
+
+
 """
     sprand([rng],[type],m,[n],p::AbstractFloat,[rfn])
 

src/sparsevector.jl

@@ -829,6 +829,26 @@ function _sparse_findprevnz(v::SparseVector, i::Integer)
     end
 end
 
+
+
+struct IterateSparseVec{T<: AbstractSparseVector} <: SparseIndexIterate
+    m::T
+end
+
+Base.eltype(::IterateSparseVec{T}) where {Ti, Tv, T <: AbstractSparseVector{Tv, Ti}} = Tuple{Ti, Tv}
+
+Base.iterate(x::IterateSparseVec, state=0) = @inbounds begin
+    state += 1
+    if state > nnz(x)
+        nothing
+    else
+        (nonzeroinds(x)[state], nonzeros(x)[state]), state
+    end
+end
+
+iternz(S::AbstractSparseVector) = IterateSparseVec(S)
+
+
 ### Generic functions operating on AbstractSparseVector
 
 ### getindex

test/sparsematrix_constructors_indexing.jl

@@ -1578,4 +1578,10 @@ end
     @test_throws ArgumentError SparseArrays.expandptr([2; 3])
 end
 
+@testset "iteratenz" begin
+    for i in 1:20
+        A = sprandn(100, 100, 1 / i)
+        @test collect(SparseArrays.iternz(A)) == collect(zip(findnz(A)...))
+    end
+end
 end

test/sparsevector.jl

@@ -338,6 +338,13 @@ end
         @test findnz(xc) == ([2, 3, 5], [1.25, 0, -0.75])
     end
 end
+
+@testset "iteratenz (vector)" begin
+    for i in 1:10
+        A = sprandn(100, i / 100)
+        @test collect(SparseArrays.iternz(A)) == collect(zip(findnz(A)...))
+    end
+end
 ### Array manipulation
 
 @testset "copy[!]" begin