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   4  * Redistribution and use in source and binary forms, with or without
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  11  *   - Redistributions in binary form must reproduce the above copyright
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  31 
  32 // Usage: jjs list_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.util.ArrayLists.
  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 
  42 var ArrayList = Java.type("java.util.ArrayList");
  43 var list = new ArrayList();
  44 list.add("nashorn");
  45 list.add("ecmascript");
  46 list.add("javascript");
  47 list.add("js");
  48 list.add("scheme");
  49 
  50 var map = Array.prototype.map;
  51 var filter = Array.prototype.filter;
  52 var reduce = Array.prototype.reduce;
  53 
  54 // sum of word lengths
  55 print("Sum word length:",
  56     reduce.call(
  57         map.call(list, function(x) x.length),
  58         function(x, y) x + y)
  59 );
  60 
  61 // filter use to filter out "j*" and concatenate rest with ":"
  62 // after uppercasing all strings
  63 print(
  64     reduce.call(
  65         map.call(
  66             filter.call(list, function(x) !x.startsWith("j")),
  67             function(x) x.toUpperCase()),
  68         function(x, y) x + ":" + y)
  69 );
  70 
  71 // another list example involving numbers
  72 list.clear();
  73 // make random list of numbers
  74 for (var i = 0; i < 10; i++)
  75     list.add(Math.random());
  76 
  77 var forEach = Array.prototype.forEach;
  78 // print numbers in the list
  79 forEach.call(list, function(x) print(x));
  80 
  81 // print sum of squares of the random numbers
  82 print("Square sum:",
  83     reduce.call(
  84         map.call(list, function(x) x*x),
  85         function(x, y) x + y)
  86 );