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