Fix findall() on sparse matrices when some stored entries are false (J…

…uliaLang#26182)

The number of returned indices needs to be adjusted in that case.

stdlib/SparseArrays/src/sparsematrix.jl

@@ -1306,14 +1306,16 @@ function findall(p::Function, S::SparseMatrixCSC)
     numnz = nnz(S)
     inds = Vector{CartesianIndex{2}}(undef, numnz)
 
-    count = 1
+    count = 0
     @inbounds for col = 1 : S.n, k = S.colptr[col] : (S.colptr[col+1]-1)
         if p(S.nzval[k])
-            inds[count] = CartesianIndex(S.rowval[k], col)
             count += 1
+            inds[count] = CartesianIndex(S.rowval[k], col)
         end
     end
 
+    resize!(inds, count)
+
     return inds
 end
 findall(p::Base.OccursIn, x::SparseMatrixCSC) =

stdlib/SparseArrays/test/sparse.jl

@@ -539,9 +539,16 @@ end
     @test length(K) == length(J) == length(V) == 2
 end
 
-@testset "issue described in https://groups.google.com/d/msg/julia-users/Yq4dh8NOWBQ/GU57L90FZ3EJ" begin
+@testset "findall" begin
+    # issue described in https://groups.google.com/d/msg/julia-users/Yq4dh8NOWBQ/GU57L90FZ3EJ
     A = sparse(I, 5, 5)
     @test findall(A) == findall(x -> x == true, A) == findall(Array(A))
+    # Non-stored entries are true
+    @test findall(x -> x == false, A) == findall(x -> x == false, Array(A))
+
+    # Not all stored entries are true
+    @test findall(sparse([true false])) == [CartesianIndex(1, 1)]
+    @test findall(x -> x > 1, sparse([1 2])) == [CartesianIndex(1, 2)]
 end
 
 @testset "issue #5824" begin