array_mapreduce.js revision 970:f82b83cf73ae 
1/*
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3 *
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11 *   - Redistributions in binary form must reproduce the above copyright
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15 *   - Neither the name of Oracle nor the names of its
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17 *     from this software without specific prior written permission.
18 *
19 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
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30 */
31
32// Usage: jjs array_mapreduce.js
33
34// Many Array.prototype functions such as map,
35// filter, reduce, reduceRight, every, some are generic.
36// These functions accept ECMAScript array as well as
37// many array-like objects including java arrays.
38// So, you can do map/filter/reduce with Java streams or
39// you can also use Array.prototype functions as below.
40// See also http://en.wikipedia.org/wiki/MapReduce
41
42var DoubleArray = Java.type("double[]");
43var StringArray = Java.type("java.lang.String[]");
44
45var map = Array.prototype.map;
46var filter = Array.prototype.filter;
47var reduce = Array.prototype.reduce;
48
49var jarr = new StringArray(5);
50jarr[0] = "nashorn";
51jarr[1] = "ecmascript";
52jarr[2] = "javascript";
53jarr[3] = "js";
54jarr[4] = "scheme";
55
56// sum of word lengths
57print("Sum word length:",
58    reduce.call(
59        map.call(jarr, function(x) x.length),
60        function(x, y) x + y)
61);
62
63// another array example involving numbers
64jarr = new DoubleArray(10);
65// make random array of numbers
66for (var i = 0; i < jarr.length; i++)
67    jarr[i] = Math.random();
68
69var forEach = Array.prototype.forEach;
70// print numbers in the array
71forEach.call(jarr, function(x) print(x));
72
73// print sum of squares of the random numbers
74print("Square sum:",
75    reduce.call(
76        map.call(jarr, function(x) x*x),
77        function(x, y) x + y)
78);
79