diff --git a/openbr/plugins/regions.cpp b/openbr/plugins/regions.cpp
index d4363b5..bd850aa 100644
--- a/openbr/plugins/regions.cpp
+++ b/openbr/plugins/regions.cpp
@@ -141,13 +141,15 @@ class CatColsTransform : public UntrainableMetaTransform
 
     void project(const Template &src, Template &dst) const
     {
+        int half = src.size()/2;
+        for (int i=0; i<half; i++) {
+            Mat first = src[i];
+            Mat second = src[half+i];
+            Mat both;
+            hconcat(first, second, both);
+            dst.append(both);
+        }
         dst.file = src.file;
-        Mat m = OpenCVUtils::toMatByRow(src);
-        // right now this just splits src in half and joins them horizontally
-        // TODO: add partitions parameter for more than a single split
-        Mat first = m.rowRange(Range(0, m.rows/2));
-        Mat second = m.rowRange(Range(m.rows/2, m.rows));
-        hconcat(first, second, dst);
     }
 };