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https://issues.apache.org/jira/browse/METRON-831?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15961906#comment-15961906
]
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_r110523411
--- 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) {
+ continue;
+ }
+ Object result = expression.apply(ImmutableList.of(o));
+ if(result != null && result instanceof Boolean && (Boolean)result)
{
+ ret.add(o);
+ }
+ }
+ return ret;
+ }
+ }
+
+ @Stellar(name="REDUCE"
+ , description="Reduces a list by a binary lambda expression.
That is, the expression takes two arguments. Usage example: REDUCE( [ 1, 2, 3
] , (x, y) -> x + y) would sum the input list, yielding 6."
+ , params = {
+ "list - List of arguments."
+ ,"binary_operation - The lambda expression function
to apply to reduce the list. It is assumed that this takes two arguments, the
first being the running total and the second being an item from the list."
+ ,"initial_value - The initial value to use."
+ }
+ , returns = "The reduction of the list."
+ )
+ public static class Reduce extends BaseStellarFunction {
+
+ @Override
+ public Object apply(List<Object> args) {
+ List<Object> input = (List<Object>) args.get(0);
+ if(input == null || input.size() < 3) {
+ return null;
+ }
+ LambdaExpression expression = (LambdaExpression) args.get(1);
+
+ Object runningResult = args.get(2);
+ if(expression == null || runningResult == null) {
+ return null;
+ }
+ for(int i = 0;i < input.size();++i) {
+ Object rhs = input.get(i);
+ if(rhs == null) {
--- End diff --
yep, we should support nulls
> 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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