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https://issues.apache.org/jira/browse/METRON-831?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15961904#comment-15961904
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ASF GitHub Bot commented on METRON-831:
---------------------------------------
Github user cestella commented on a diff in the pull request:
https://github.com/apache/incubator-metron/pull/517#discussion_r110523398
--- Diff:
metron-platform/metron-common/src/main/java/org/apache/metron/common/dsl/functions/FunctionalFunctions.java
---
@@ -0,0 +1,121 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (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.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.metron.common.dsl.functions;
+
+import com.google.common.collect.ImmutableList;
+import org.apache.metron.common.dsl.BaseStellarFunction;
+import org.apache.metron.common.dsl.Stellar;
+import org.apache.metron.common.stellar.LambdaExpression;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class FunctionalFunctions {
+ @Stellar(name="MAP"
+ , description="Applies lambda expression to a list of arguments.
e.g. MAP( [ 'foo', 'bar' ] , ( x ) -> TO_UPPER(x) ) would yield [ 'FOO', 'BAR'
]"
+ , params = {
+ "list - List of arguments."
+ ,"transform_expression - The lambda expression to
apply. This expression is assumed to take one argument."
+ }
+ , returns = "The input list transformed item-wise by the lambda
expression."
+ )
+ public static class Map extends BaseStellarFunction {
+
+ @Override
+ public Object apply(List<Object> args) {
+ List<Object> input = (List<Object>) args.get(0);
+ LambdaExpression expression = (LambdaExpression)args.get(1);
+ if(input == null || expression == null) {
+ return input;
+ }
+ List<Object> ret = new ArrayList<>();
+ for(Object o : input) {
+ if(o != null) {
+ ret.add(expression.apply(ImmutableList.of(o)));
+ }
+ }
+ return ret;
+ }
+ }
+
+ @Stellar(name="FILTER"
+ , description="Applies a filter in the form of a lambda
expression to a list. e.g. FILTER( [ 'foo', 'bar' ] , (x) -> x == 'foo') would
yield [ 'foo']"
+ , params = {
+ "list - List of arguments."
+ ,"predicate - The lambda expression to apply. This
expression is assumed to take one argument and return a boolean."
+ }
+ , returns = "The input list filtered by the predicate."
+ )
+ public static class Filter extends BaseStellarFunction {
+
+ @Override
+ public Object apply(List<Object> args) {
+ List<Object> input = (List<Object>) args.get(0);
+ LambdaExpression expression = (LambdaExpression) args.get(1);
+ if(input == null || expression == null) {
+ return input;
+ }
+ List<Object> ret = new ArrayList<>();
+ for(Object o : input) {
+ if(o == null) {
--- End diff --
yes, your example should work and return `[null]`
> Add lambda expressions and rudimentary functional programming primitives to
> Stellar
> -----------------------------------------------------------------------------------
>
> Key: METRON-831
> URL: https://issues.apache.org/jira/browse/METRON-831
> Project: Metron
> Issue Type: Improvement
> Reporter: Casey Stella
>
> To enable use-cases where the user may want to do simple iteration, we can
> expose simple functional primitives such as:
> * MAP
> * REDUCE
> * FILTER
> To fully support this, we will need lambda expressions as arguments to these
> functions.
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