feat: introduce transform and reduce invocation function for lambdas

ksqldb-engine/src/main/java/io/confluent/ksql/function/udf/lambda/Reduce.java

@@ -0,0 +1,96 @@
+/*
+ * Copyright 2021 Confluent Inc.
+ *
+ * Licensed under the Confluent Community License (the "License"; you may not use
+ * this file except in compliance with the License. You may obtain a copy of the
+ * License at
+ *
+ * http://www.confluent.io/confluent-community-license
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OF ANY KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations under the License.
+ */
+
+package io.confluent.ksql.function.udf.lambda;
+
+import io.confluent.ksql.execution.codegen.helpers.TriFunction;
+import io.confluent.ksql.function.FunctionCategory;
+import io.confluent.ksql.function.udf.Udf;
+import io.confluent.ksql.function.udf.UdfDescription;
+import io.confluent.ksql.function.udf.UdfParameter;
+import io.confluent.ksql.util.KsqlConstants;
+import java.util.List;
+import java.util.Map;
+import java.util.Map.Entry;
+import java.util.function.BiFunction;
+
+/**
+ * Reduce a collection using an initial state and function
+ */
+@UdfDescription(
+    name = "reduce",
+    category = FunctionCategory.LAMBDA,
+    description = "Reduce the input collection down to a single value " 
+        + "using an initial state and a function. " 
+        + "The initial state (s) is passed into the scope of the function. " 
+        + "Each invocation returns a new value for s, " 
+        + "which the next invocation will receive. "  
+        + "The final value for s is returned.",
+    author = KsqlConstants.CONFLUENT_AUTHOR
+)
+public class Reduce {
+
+  @Udf(description = "When reducing an array, "
+      + "the reduce function must have two arguments. "
+      + "The two arguments for the reduce function are in order: "
+      + "the array item and the state. "
+      + "The final state is returned."
+  )
+  public <T,S> S reduceArray(
+      @UdfParameter(description = "The initial state.") final S initialState,
+      @UdfParameter(description = "The array.") final List<T> list,
+      @UdfParameter(description = "The reduce function.") final BiFunction<S, T, S> biFunction
+  ) {
+    if (initialState == null) {
+      return null;
+    }
+
+    if (list == null) {
+      return initialState;
+    }
+
+    S state = initialState;
+    for (T listItem: list) {
+      state = biFunction.apply(state, listItem);
+    }
+    return state;
+  }
+
+  @Udf(description = "When reducing a map, " 
+      + "the reduce function must have three arguments. "
+      + "The three arguments for the reduce function are in order: " 
+      + "the key, the value, and the state. "
+      + "The final state is returned."
+  )
+  public <K,V,S> S reduceMap(
+      @UdfParameter(description = "The initial state.") final S initialState,
+      @UdfParameter(description = "The map.") final Map<K, V> map,
+      @UdfParameter(description = "The reduce function.") final TriFunction<S, K, V, S> triFunction
+  ) {
+    if (initialState == null) {
+      return null;
+    }
+
+    if (map == null) {
+      return initialState;
+    }
+
+    S state = initialState;
+    for (Entry<K, V> entry : map.entrySet()) {
+      state = triFunction.apply(state, entry.getKey(), entry.getValue());
+    }
+    return state;
+  }
+}

ksqldb-engine/src/main/java/io/confluent/ksql/function/udf/map/MapTransform.java → ksqldb-engine/src/main/java/io/confluent/ksql/function/udf/lambda/Transform.java

@@ -13,35 +13,56 @@
  * specific language governing permissions and limitations under the License.
  */
 
-package io.confluent.ksql.function.udf.map;
+package io.confluent.ksql.function.udf.lambda;
 
 import io.confluent.ksql.function.FunctionCategory;
 import io.confluent.ksql.function.udf.Udf;
 import io.confluent.ksql.function.udf.UdfDescription;
 import io.confluent.ksql.function.udf.UdfParameter;
 import io.confluent.ksql.util.KsqlConstants;
+import java.util.List;
 import java.util.Map;
 import java.util.function.BiFunction;
+import java.util.function.Function;
 import java.util.stream.Collectors;
 
 /**
- * Transform a map's key and values using two lambda functions
+ * Transform a collection with a function
  */
 @UdfDescription(
-    name = "map_transform",
-    category = FunctionCategory.MAP,
-    description = "Apply one function to each key and " 
-        + "one function to each value of a map. " 
-        + "The two arguments for each function are in order: key, value. " 
-        + "The first function provided will be applied to each key and the " 
-        + "second one applied to each value. "
-        + "The transformed map is returned.",
+    name = "transform",
+    category = FunctionCategory.LAMBDA,
+    description = "Apply a function to each element in a collection. " 
+        + "The transformed collection is returned.",
     author = KsqlConstants.CONFLUENT_AUTHOR
 )
-public class MapTransform {
+public class Transform {
 
-  @Udf
-  public <K,V,R,T> Map<R,T> mapTransform(
+  @Udf(description = "When transforming an array, "
+      + "the function provided must have two arguments. "
+      + "The two arguments for each function are in order: " 
+      + "the key and then the value. "
+      + "The transformed array is returned."
+  )
+  public <T, R> List<R> transformArray(
+      @UdfParameter(description = "The array") final List<T> array,
+      @UdfParameter(description = "The lambda function") final Function<T, R> function
+  ) {
+    if (array == null) {
+      return null;
+    }
+    return array.stream().map(function::apply).collect(Collectors.toList());
+  }
+
+  @Udf(description = "When transforming a map, "
+      + "two functions must be provided. "
+      + "For each map entry, the first function provided will "
+      + "be applied to the key and the second one applied to the value. "
+      + "Each function must have two arguments. "
+      + "The two arguments for each function are in order: the key and then the value. "
+      + "The transformed map is returned."
+  )
+  public <K,V,R,T> Map<R,T> transformMap(
       @UdfParameter(description = "The map") final Map<K, V> map,
       @UdfParameter(description = "The key lambda function") final BiFunction<K, V, R> biFunction1,
       @UdfParameter(description = "The value lambda function") final BiFunction<K, V, T> biFunction2