diff --git a/src/main/java/de/ids_mannheim/korap/resource/rewrite/CollectionCleanRewrite.java b/src/main/java/de/ids_mannheim/korap/resource/rewrite/CollectionCleanRewrite.java
new file mode 100644
index 0000000..0d5e691
--- /dev/null
+++ b/src/main/java/de/ids_mannheim/korap/resource/rewrite/CollectionCleanRewrite.java
@@ -0,0 +1,73 @@
+package de.ids_mannheim.korap.resource.rewrite;
+
+import com.fasterxml.jackson.databind.JsonNode;
+import com.fasterxml.jackson.databind.node.ObjectNode;
+import de.ids_mannheim.korap.config.BeanInjectable;
+import de.ids_mannheim.korap.config.ContextHolder;
+import de.ids_mannheim.korap.config.KustvaktConfiguration;
+import de.ids_mannheim.korap.user.User;
+import de.ids_mannheim.korap.utils.JsonUtils;
+import edu.emory.mathcs.backport.java.util.Arrays;
+
+import java.util.Iterator;
+
+/**
+ * @author hanl
+ * @date 28/07/2015
+ */
+public class CollectionCleanRewrite implements RewriteTask.RewriteNodeAt {
+
+    @Override
+    public JsonNode rewriteQuery (KoralNode node, KustvaktConfiguration config,
+            User user) {
+        return process(node.rawNode());
+    }
+
+
+    private JsonNode process (JsonNode root) {
+        JsonNode sub = root;
+        if (root.isObject()) {
+            if (root.has("operands")) {
+                JsonNode node = root.at("/operands");
+                Iterator<JsonNode> it = node.elements();
+                while (it.hasNext()) {
+                    JsonNode n = it.next();
+                    JsonNode s = process(n);
+                    if (s == null)
+                        it.remove();
+                }
+
+                int count = node.size();
+                // remove group element and replace with single doc
+                if (count == 1)
+                    sub = node.path(0);
+                // indicate empty group
+                else if (count == 0) // can't do anything here -- fixme: edge case?!
+                    return null;
+            }
+
+            // what happens to array nodes?
+            if (!root.equals(sub)) {
+                if (sub.isObject()) {
+                    ObjectNode ob = (ObjectNode) root;
+                    ob.remove(Arrays.asList(new String[] { "@type",
+                            "operation", "operands" }));
+                    ob.putAll((ObjectNode) sub);
+                }
+            }
+        }
+        return root;
+    }
+
+
+    @Override
+    public JsonNode rewriteResult (KoralNode node) {
+        return null;
+    }
+
+
+    @Override
+    public String at () {
+        return "/collection";
+    }
+}