diff --git a/sklearn2pmml/cross_reference/__init__.py b/sklearn2pmml/cross_reference/__init__.py
index 41f20e3..99d27bb 100644
--- a/sklearn2pmml/cross_reference/__init__.py
+++ b/sklearn2pmml/cross_reference/__init__.py
@@ -1,7 +1,20 @@
 from sklearn.base import BaseEstimator, TransformerMixin
+from sklearn.pipeline import FeatureUnion
 
 import numpy
 
+def make_memorizer_union(memory, names):
+	return FeatureUnion([
+		("memorizer", Memorizer(memory, names)),
+		("passthrough", "passthrough"),
+	])
+
+def make_recaller_union(memory, names):
+	return FeatureUnion([
+		("recaller", Recaller(memory, names)),
+		("passthrough", "passthrough")
+	])
+
 class _BaseMemoryManager(BaseEstimator, TransformerMixin):
 
 	def __init__(self, memory, names):
diff --git a/sklearn2pmml/cross_reference/tests/__init__.py b/sklearn2pmml/cross_reference/tests/__init__.py
index 2f65453..b344b8a 100644
--- a/sklearn2pmml/cross_reference/tests/__init__.py
+++ b/sklearn2pmml/cross_reference/tests/__init__.py
@@ -1,5 +1,5 @@
 from pandas import DataFrame
-from sklearn2pmml.cross_reference import Memorizer, Recaller
+from sklearn2pmml.cross_reference import make_memorizer_union, make_recaller_union, Memorizer, Recaller
 from unittest import TestCase
 
 import numpy
@@ -32,12 +32,11 @@ def test_fit_transform(self):
 class RecallerTest(TestCase):
 
 	def test_fit_transform(self):
-		X = numpy.empty((100, 5), dtype = str)
-
 		memory = {
 			"int": [-1, 1]
 		}
 		recaller = Recaller(memory, ["int"])
+		X = numpy.empty((2, 1), dtype = str)
 		Xt = recaller.fit_transform(X)
 		self.assertEqual((2, 1), Xt.shape)
 		self.assertEqual([-1, 1], Xt[:, 0].tolist())
@@ -45,6 +44,7 @@ def test_fit_transform(self):
 		memory = DataFrame([[1, 1.0, "one"], [2, 2.0, "two"], [3, 3.0, "three"]], columns = ["int", "float", "str"])
 		self.assertEqual((3, 3), memory.shape)
 		recaller = Recaller(memory, ["int"])
+		X = numpy.empty((3, 5), dtype = str)
 		Xt = recaller.fit_transform(X)
 		self.assertEqual((3, 1), Xt.shape)
 		self.assertEqual([1, 2, 3], Xt[:, 0].tolist())
@@ -54,3 +54,26 @@ def test_fit_transform(self):
 		self.assertEqual([1, 2, 3], Xt[:, 0].tolist())
 		self.assertEqual([1.0, 2.0, 3.0], Xt[:, 1].tolist())
 		self.assertEqual(["one", "two", "three"], Xt[:, 2].tolist())
+
+class FunctionTest(TestCase):
+
+	def test_make_memorizer_union(self):
+		memory = dict()
+		self.assertEqual(0, len(memory))
+		memorizer = make_memorizer_union(memory, ["int"])
+		X = numpy.asarray([[-1], [1]])
+		Xt = memorizer.fit_transform(X)
+		self.assertEqual((2, 1), Xt.shape)
+		self.assertEqual(1, len(memory))
+		self.assertEqual([-1, 1], memory["int"].tolist())
+
+	def test_make_recaller_union(self):
+		memory = {
+			"int": [-1, 1]
+		}
+		recaller = make_recaller_union(memory, ["int"])
+		X = numpy.full((2, 1), 0, dtype = int)
+		Xt = recaller.fit_transform(X)
+		self.assertEqual((2, 2), Xt.shape)
+		self.assertEqual([-1, 1], Xt[:, 0].tolist())
+		self.assertEqual([0, 0], Xt[:, 1].tolist())