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