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/*
* 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
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
* LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
* NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
* 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)
);
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