Added an append function such that JSON can be appended to the current document and then a function executed over the result.

json-path/src/main/java/com/jayway/jsonpath/internal/function/PathFunctionFactory.java

@@ -2,6 +2,7 @@ package com.jayway.jsonpath.internal.function;
 
 import com.jayway.jsonpath.InvalidPathException;
 import com.jayway.jsonpath.internal.function.http.HttpLoader;
+import com.jayway.jsonpath.internal.function.json.Append;
 import com.jayway.jsonpath.internal.function.numeric.Average;
 import com.jayway.jsonpath.internal.function.numeric.Max;
 import com.jayway.jsonpath.internal.function.numeric.Min;
@@ -47,6 +48,7 @@ public class PathFunctionFactory {
         // JSON Entity Functions
         map.put("length", Length.class);
         map.put("size", Length.class);
+        map.put("append", Append.class);
 
 
         FUNCTIONS = Collections.unmodifiableMap(map);

json-path/src/main/java/com/jayway/jsonpath/internal/function/json/Append.java

@@ -0,0 +1,31 @@
+package com.jayway.jsonpath.internal.function.json;
+
+import com.jayway.jsonpath.internal.EvaluationContext;
+import com.jayway.jsonpath.internal.PathRef;
+import com.jayway.jsonpath.internal.function.Parameter;
+import com.jayway.jsonpath.internal.function.PathFunction;
+import com.jayway.jsonpath.spi.json.JsonProvider;
+
+import java.util.List;
+
+/**
+ * Appends JSON structure to the current document so that you can utilize the JSON added thru another function call.
+ * If there are multiple parameters then this function call will add each element that is json to the structure
+ *
+ * Created by mgreenwood on 12/14/15.
+ */
+public class Append implements PathFunction {
+    @Override
+    public Object invoke(String currentPath, PathRef parent, Object model, EvaluationContext ctx, List<Parameter> parameters) {
+        JsonProvider jsonProvider = ctx.configuration().jsonProvider();
+        if (parameters != null && parameters.size() > 0) {
+            for (Parameter param : parameters) {
+                if (jsonProvider.isArray(model)) {
+                    int len = jsonProvider.length(model);
+                    jsonProvider.setArrayIndex(model, len, param.getCachedValue());
+                }
+            }
+        }
+        return model;
+    }
+}

json-path/src/test/java/com/jayway/jsonpath/internal/function/NestedFunctionTest.java

@@ -69,4 +69,9 @@ public class NestedFunctionTest extends BaseFunctionTest {
     public void testLoadFunction() {
         verifyTextFunction(conf, "$.getjson($.urls[0])[0].total", 264);
     }
+
+    @Test
+    public void testAppendNumber() {
+        verifyMathFunction(conf, "$.numbers.append(11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 0).avg()", 10.0);
+    }
 }