Don't use _mapreduce for countnz

base/reduce.jl

@@ -407,13 +407,17 @@ function count(pred, A::AbstractArray)
     return n
 end
 
-immutable NotEqZero <: Func{1} end
-call(::NotEqZero, x) = x != 0
-
 """
     countnz(A)
 
 Counts the number of nonzero values in array `A` (dense or sparse). Note that this is not a constant-time operation.
 For sparse matrices, one should usually use `nnz`, which returns the number of stored values.
 """
-countnz(a) = count(NotEqZero(), a)
+function countnz(a)
+    n = 0
+    @inbounds for i in eachindex(a)
+        ai = a[i]
+        n = ifelse(ai == zero(ai), n, n + 1)
+    end
+    return n
+end