fast extrema computation on sparse arrays

Author: Clément Fauchereau

stdlib/SparseArrays/src/SparseArrays.jl

@@ -18,7 +18,7 @@ import LinearAlgebra: mul!, ldiv!, rdiv!, cholesky, adjoint!, diag, eigen, dot,
 import Base: acos, acosd, acot, acotd, acsch, asech, asin, asind, asinh,
     atan, atand, atanh, broadcast!, conj!, cos, cosc, cosd, cosh, cospi, cot,
     cotd, coth, count, csc, cscd, csch,
-    exp10, exp2, findprev, findnext, floor, hash, argmin, inv,
+    exp10, exp2, extrema, findprev, findnext, floor, hash, argmin, inv,
     log10, log2, sec, secd, sech, show,
     sin, sinc, sind, sinh, sinpi, dropdims, sum, summary, tan,
     tand, tanh, trunc, abs, abs2,

stdlib/SparseArrays/src/sparsematrix.jl

@@ -3742,3 +3742,20 @@ end
 
 circshift!(O::AbstractSparseMatrixCSC, X::AbstractSparseMatrixCSC, (r,)::Base.DimsInteger{1}) = circshift!(O, X, (r,0))
 circshift!(O::AbstractSparseMatrixCSC, X::AbstractSparseMatrixCSC, r::Real) = circshift!(O, X, (Integer(r),0))
+
+function extrema(f, A::AbstractSparseMatrixCSC)
+    if iszero(length(A))
+        throw(ArgumentError("Sparse matrix must have at least one element."))
+    end
+    N = nnz(A)
+    iszero(N) && return f(zero(eltype(A))), f(zero(eltype(A)))
+    vmin, vmax = extrema(f, nonzeros(A))
+    if N != length(A)
+        f0 = f(zero(eltype(A)))
+        vmin = min(f0, vmin)
+        vmax = max(f0, vmax)
+    end
+    vmin, vmax
+end
+
+extrema(A::AbstractSparseMatrixCSC) = extrema(identity, A)

stdlib/SparseArrays/src/sparsevector.jl

@@ -2122,3 +2122,20 @@ end
 
 
 circshift!(O::SparseVector, X::SparseVector, r::Real,) = circshift!(O, X, (Integer(r),))
+
+function extrema(f, A::AbstractSparseVector)
+    if length(A) == 0
+        throw(ArgumentError("Sparse vector must have at least one element."))
+    end
+    N = nnz(A)
+    iszero(N) && return f(zero(eltype(A))), f(zero(eltype(A)))
+    vmin, vmax = extrema(f, nonzeros(A))
+    if N != length(A)
+        f0 = f(zero(eltype(A)))
+        vmin = min(f0, vmin)
+        vmax = max(f0, vmax)
+    end
+    vmin, vmax
+end
+
+extrema(A::AbstractSparseVector) = extrema(identity, A)

stdlib/SparseArrays/test/sparse.jl

@@ -3082,4 +3082,16 @@ end
     @test nonzeros(d) == V[1:4]
 end
 
+@testset "extrema" begin
+    n = 10
+    A = sprand(n, n, 0.2)
+    B = Array(A)
+    f(x) = x^3
+    @test extrema(A) == extrema(B)
+    @test extrema(f, A) == extrema(f, B)
+    @test extrema(spzeros(n, n)) == (0.0, 0.0)
+    @test_throws ArgumentError extrema(spzeros(0, 0))
+    @test extrema(sparse(ones(n, n))) == (1.0, 1.0)
+end
+
 end # module

stdlib/SparseArrays/test/sparsevector.jl

@@ -1457,4 +1457,16 @@ end
     end
 end
 
+@testset "extrema" begin
+    n = 10
+    A = sprand(n, 0.2)
+    B = Array(A)
+    f(x) = x^3
+    @test extrema(A) == extrema(B)
+    @test extrema(f, A) == extrema(f, B)
+    @test extrema(spzeros(n)) == (0.0, 0.0)
+    @test_throws ArgumentError extrema(spzeros(0))
+    @test extrema(sparse(ones(n))) == (1.0, 1.0)
+end
+
 end # module