| /* |
| * Copyright (c) 2014, Oracle and/or its affiliates. All rights reserved. |
| * |
| * Redistribution and use in source and binary forms, with or without |
| * modification, are permitted provided that the following conditions |
| * are met: |
| * |
| * - Redistributions of source code must retain the above copyright |
| * notice, this list of conditions and the following disclaimer. |
| * |
| * - Redistributions in binary form must reproduce the above copyright |
| * notice, this list of conditions and the following disclaimer in the |
| * documentation and/or other materials provided with the distribution. |
| * |
| * - Neither the name of Oracle nor the names of its |
| * contributors may be used to endorse or promote products derived |
| * from this software without specific prior written permission. |
| * |
| * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS |
| * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, |
| * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR |
| * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR |
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| * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. |
| */ |
| |
| // Usage: jjs list_mapreduce.js |
| |
| // Many Array.prototype functions such as map, |
| // filter, reduce, reduceRight, every, some are generic. |
| // These functions accept ECMAScript array as well as |
| // many array-like objects including java.util.ArrayLists. |
| // So, you can do map/filter/reduce with Java streams or |
| // you can also use Array.prototype functions as below. |
| // See also http://en.wikipedia.org/wiki/MapReduce |
| |
| var ArrayList = Java.type("java.util.ArrayList"); |
| var list = new ArrayList(); |
| list.add("nashorn"); |
| list.add("ecmascript"); |
| list.add("javascript"); |
| list.add("js"); |
| list.add("scheme"); |
| |
| var map = Array.prototype.map; |
| var filter = Array.prototype.filter; |
| var reduce = Array.prototype.reduce; |
| |
| // sum of word lengths |
| print("Sum word length:", |
| reduce.call( |
| map.call(list, function(x) x.length), |
| function(x, y) x + y) |
| ); |
| |
| // filter use to filter out "j*" and concatenate rest with ":" |
| // after uppercasing all strings |
| print( |
| reduce.call( |
| map.call( |
| filter.call(list, function(x) !x.startsWith("j")), |
| function(x) x.toUpperCase()), |
| function(x, y) x + ":" + y) |
| ); |
| |
| // another list example involving numbers |
| list.clear(); |
| // make random list of numbers |
| for (var i = 0; i < 10; i++) |
| list.add(Math.random()); |
| |
| var forEach = Array.prototype.forEach; |
| // print numbers in the list |
| forEach.call(list, function(x) print(x)); |
| |
| // print sum of squares of the random numbers |
| print("Square sum:", |
| reduce.call( |
| map.call(list, function(x) x*x), |
| function(x, y) x + y) |
| ); |