Lists


List

Lists (or arrays) are simple sequence of objects, their size is dynamic and their index starts always at 0. They provide fast random access to their elements. You can create a list by placing a sequence of comma-separated expressions inside square brackets:

    var r = [1, 2, "Hello", 3.1415, true];

    // list has a count property
    var n = r.count;    // n is 5

Accessing elements

You can access an element from a list by calling the subscript operator [] on it with the index of the element you want. Like most languages, indices start at 0:

    var names = ["Mark", "Andrew", "Paul", "Ross", "Frank", "Max"];
    names[0];   // "Mark"
    names[2];   // "Paul"

Negative indices count backwards from the end:

    var names = ["Mark", "Andrew", "Paul", "Ross", "Frank", "Max"];
    names[-1];  // "Max"
    names[-2];  // "Frank"

Iterating elements

The subscript operator works well for finding values when you know the key you’re looking for, but sometimes you want to see everything that’s in the list. Since the List class implements the iterator method, you can easily use it in a for loop:

    var people = ["Mark", "Andrew", "Paul", "Ross", "Frank", "Max"];
    for (var name in people) {
        System.print("Current name is " + name);
    }

Adding elements

A List instance can be expanded by setting an index that is greater than the current size of the list:

    var list = [10,20,30,40,50];
    list[30] = 22;  // list contains now 31 elements (index 0...30)

List as a stack

The List class implements the push/pop methods as a convenient way to treat a list as a stack:

    var list = [10,20,30,40,50];
    list.push(100);     // add 100 to the list
    var v1 = list.pop();    // pop 100
    var v2 = list.pop();    // pop 50

List Contains

The List class implements the contains methods as a convenient way to check for the existence of a value in a list:

    var list = [1, 2, "Hello", 3.1415, true];
    return list.contains(3.1415); // Returns: true

List Joins

The List class implements the join method as a convenient way to interpret a list as a string:

    var list = [1,2,3,4,5];
    list.join(" + "); // Becomes: "1 + 2 + 3 + 4 + 5"

List Map

The List class implements the map method as a convenient way to create a new list using the current values of a list in some defined way:

  var numbers = [1,2,3,4,5,6,7,8,9,10]

  var squared = numbers.map(func(num) {
    return num*num
  })
  // squared is now equal to [1,4,9,16,25,36,49,64,81,100]

List Filter

The List class implements the filter method as a convenient way to create a new list that contains the elements of the original list which passed a specified test:

  var numbers = [1,2,3,4,5,6,7,8,9,10]

  var even = numbers.map(func(num) {
    return !(num % 2)
  })
  // even is now equal to [2,4,6,8,10]

List Reduce

The List class implements the reduce method as a convenient way to create a new list reduces a list to a single value based on a provided callback:

  var numbers = [1,2,3,4,5,6,7,8,9,10]

  var sum = numbers.reduce(0, func(num1, num2) {
    return num1+num2
  })
  // sum is now equal to 55