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  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 
  42 var DoubleArray = Java.type("double[]");
  43 var StringArray = Java.type("java.lang.String[]");
  44 
  45 var map = Array.prototype.map;
  46 var filter = Array.prototype.filter;
  47 var reduce = Array.prototype.reduce;
  48 
  49 var jarr = new StringArray(5);
  50 jarr[0] = "nashorn";
  51 jarr[1] = "ecmascript";
  52 jarr[2] = "javascript";
  53 jarr[3] = "js";
  54 jarr[4] = "scheme";
  55 
  56 // sum of word lengths
  57 print("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
  64 jarr = new DoubleArray(10);
  65 // make random array of numbers
  66 for (var i = 0; i < jarr.length; i++)
  67     jarr[i] = Math.random();
  68 
  69 var forEach = Array.prototype.forEach;
  70 // print numbers in the array
  71 forEach.call(jarr, function(x) print(x));
  72 
  73 // print sum of squares of the random numbers
  74 print("Square sum:",
  75     reduce.call(
  76         map.call(jarr, function(x) x*x),
  77         function(x, y) x + y)
  78 );