Add ==(::NullableArray, ::NullableArray)

Fixes JuliaStats#82.

src/primitives.jl

@@ -134,6 +134,30 @@ Returns the last entry of `X`.
 """ ->
 Base.endof(X::NullableArray) = endof(X.values) # -> Int
 
+@doc """
+`==(A::NullableArray, B::NullableArray)`
+
+When none of the arrays contains a missing values, returns `Nullable(true)`
+if all elements of the two arrays are equal according to `==`, and
+`Nullable(false)` otherwise. Returns `Nullable{Bool}()` if one of the arrays
+contains a missing value.
+""" ->
+function Base.(:(==))(A::NullableArray, B::NullableArray)
+    if size(A) != size(B)
+        return false
+    end
+    # Short-circuit is only possible after finding a missing element
+    ret = true
+    for i in eachindex(A,B)
+        if A.isnull[i] || B.isnull[i]
+            return Nullable{Bool}()
+        elseif A.values[i] != B.values[i]
+            ret = false
+        end
+    end
+    return Nullable(ret)
+end
+
 @doc """
 
 """ ->

test/primitives.jl

@@ -149,6 +149,17 @@ module TestPrimitives
     @test endof(NullableArray(collect(1:10))) == 10
     @test endof(NullableArray([1, 2, nothing, 4, nothing])) == 5
 
+# ----- test Base.== ------------------------------------------------------#
+    x = NullableArray(collect(1:3))
+    @test get(x == NullableArray([1.0, 2.0, 3.0]))
+    @test get(x != NullableArray([1.1, 2.0, 3.0]))
+    y = NullableArray([1.0, 2.0, 3.0], [false, false, true])
+    z = NullableArray([1.1, 2.0, 3.0], [false, true, false])
+    @test isnull(x == y)
+    @test isnull(x != y)
+    @test isnull(x == z)
+    @test isnull(x != z)
+
 # ----- test Base.find -------------------------------------------------------#
 
     z = NullableArray(rand(Bool, 10))