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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 );