Allow any f for sum/minimum/maximum(f, v::AbstractSparseVector) (#29884)

* sum/minimum/maximum(f, v::AbstractSparseVector)

generalize sum/minimum/maximum(abs/abs2, v::AbstractSparseVector) to
arbitrary f

* add broken sum(f, [])==0 tests for reference

stdlib/SparseArrays/src/sparsevector.jl

@@ -1354,34 +1354,50 @@ end
 
 ### Reduction
 
+function _sum(f, x::AbstractSparseVector)
+    n = length(x)
+    n > 0 || return sum(f, nonzeros(x)) # return zero() of proper type
+    m = nnz(x)
+    (m == 0 ? n * f(zero(eltype(x))) :
+     m == n ? sum(f, nonzeros(x)) :
+     Base.add_sum((n - m) * f(zero(eltype(x))), sum(f, nonzeros(x))))
+end
+
+sum(f::Union{Function, Type}, x::AbstractSparseVector) = _sum(f, x) # resolve ambiguity
+sum(f, x::AbstractSparseVector) = _sum(f, x)
 sum(x::AbstractSparseVector) = sum(nonzeros(x))
 
-function maximum(x::AbstractSparseVector{T}) where T<:Real
+function _maximum(f, x::AbstractSparseVector)
     n = length(x)
-    n > 0 || throw(ArgumentError("maximum over empty array is not allowed."))
+    if n == 0
+        if f === abs || f === abs2
+            return zero(eltype(x)) # preserving maximum(abs/abs2, x) behaviour in 1.0.x
+        else
+            throw(ArgumentError("maximum over an empty array is not allowed."))
+        end
+    end
     m = nnz(x)
-    (m == 0 ? zero(T) :
-     m == n ? maximum(nonzeros(x)) :
-     max(zero(T), maximum(nonzeros(x))))::T
+    (m == 0 ? f(zero(eltype(x))) :
+     m == n ? maximum(f, nonzeros(x)) :
+     max(f(zero(eltype(x))), maximum(f, nonzeros(x))))
 end
 
-function minimum(x::AbstractSparseVector{T}) where T<:Real
+maximum(f::Union{Function, Type}, x::AbstractSparseVector) = _maximum(f, x) # resolve ambiguity
+maximum(f, x::AbstractSparseVector) = _maximum(f, x)
+maximum(x::AbstractSparseVector) = maximum(identity, x)
+
+function _minimum(f, x::AbstractSparseVector)
     n = length(x)
-    n > 0 || throw(ArgumentError("minimum over empty array is not allowed."))
+    n > 0 || throw(ArgumentError("minimum over an empty array is not allowed."))
     m = nnz(x)
-    (m == 0 ? zero(T) :
-     m == n ? minimum(nonzeros(x)) :
-     min(zero(T), minimum(nonzeros(x))))::T
+    (m == 0 ? f(zero(eltype(x))) :
+     m == n ? minimum(f, nonzeros(x)) :
+     min(f(zero(eltype(x))), minimum(f, nonzeros(x))))
 end
 
-for f in [:sum, :maximum, :minimum], op in [:abs, :abs2]
-    SV = :AbstractSparseVector
-    if f === :minimum
-        @eval ($f)(::typeof($op), x::$SV{T}) where {T<:Number} = nnz(x) < length(x) ? ($op)(zero(T)) : ($f)($op, nonzeros(x))
-    else
-        @eval ($f)(::typeof($op), x::$SV) = ($f)($op, nonzeros(x))
-    end
-end
+minimum(f::Union{Function, Type}, x::AbstractSparseVector) = _minimum(f, x) # resolve ambiguity
+minimum(f, x::AbstractSparseVector) = _minimum(f, x)
+minimum(x::AbstractSparseVector) = minimum(identity, x)
 
 norm(x::SparseVectorUnion, p::Real=2) = norm(nonzeros(x), p)
 

stdlib/SparseArrays/test/sparsevector.jl

@@ -789,6 +789,19 @@ end
     @test sum(x) == 4.0
     @test sum(abs, x) == 5.5
     @test sum(abs2, x) == 14.375
+    @test @inferred(sum(t -> true, x)) === 8
+    @test @inferred(sum(t -> abs(t) + one(t), x)) == 13.5
+
+    @test @inferred(sum(t -> true, spzeros(Float64, 8))) === 8
+    @test @inferred(sum(t -> abs(t) + one(t), spzeros(Float64, 8))) === 8.0
+
+    # reducing over an empty collection
+    # FIXME sum(f, []) throws, should be fixed both for generic and sparse vectors
+    @test_broken sum(t -> true, zeros(Float64, 0)) === 0
+    @test_broken sum(t -> true, spzeros(Float64, 0)) === 0
+    @test @inferred(sum(abs2, spzeros(Float64, 0))) === 0.0
+    @test_broken sum(t -> abs(t) + one(t), zeros(Float64, 0)) === 0.0
+    @test_broken sum(t -> abs(t) + one(t), spzeros(Float64, 0)) === 0.0
 
     @test norm(x) == sqrt(14.375)
     @test norm(x, 1) == 5.5
@@ -802,6 +815,12 @@ end
         @test minimum(x) == -0.75
         @test maximum(abs, x) == 3.5
         @test minimum(abs, x) == 0.0
+        @test @inferred(minimum(t -> true, x)) === true
+        @test @inferred(maximum(t -> true, x)) === true
+        @test @inferred(minimum(t -> abs(t) + one(t), x)) == 1.0
+        @test @inferred(maximum(t -> abs(t) + one(t), x)) == 4.5
+        @test @inferred(minimum(t -> t + one(t), x)) == 0.25
+        @test @inferred(maximum(t -> -abs(t) + one(t), x)) == 1.0
     end
 
     let x = abs.(spv_x1)
@@ -826,6 +845,15 @@ end
         @test minimum(x) == 0.0
         @test maximum(abs, x) == 0.0
         @test minimum(abs, x) == 0.0
+        @test @inferred(minimum(t -> true, x)) === true
+        @test @inferred(maximum(t -> true, x)) === true
+        @test @inferred(minimum(t -> abs(t) + one(t), x)) === 1.0
+        @test @inferred(maximum(t -> abs(t) + one(t), x)) === 1.0
+    end
+
+    let x = spzeros(Float64, 0)
+        @test_throws ArgumentError minimum(t -> true, x)
+        @test_throws ArgumentError maximum(t -> true, x)
     end
 end