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// 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)

);