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Creating Arrays

• var empty =[];
• var primes = [2, 3, 5, 7, 11];
• var a = new Array();
• var a = new Array(10); //a.length is 10
• var a = new Array(5, 4, 3, 2, 1, "testing", "testing");

Reading and Writing Array Elements

• value = a[0];
• a[1] = 3.14;
• i = 2;
  a[i] = 3;
  a[i+1]="hello";
  a[a[i]]=a[0];
• Indices
  a["10"] // is the 11th element
  a[1.00] // is same as a[1]
  a[a.length] // is undefined

Adding and deleting array elements

• As above
  a=[] //empty array
  a[0] = "hello" //adds an element
• using push
  a=[] //empty array
  a.push("hello") //adds an element
• using delete to delete item at index number
  a=[1,2,3] //array of 3 elements
  delete a[1]; //deletes element at index 1
  1 in a // returns false. no element defined at index 1
  a.length // still 3. Just undefined element

Iterating Arrays

• for loop used

  a=[1,2,3];
  for (i=0; i < a.length; i++) {
    //loop body
  }
  

• See examples on pages 146 and 147

Array of images

• Arrays use [ ]
• document.images[ ]
• Code used on images.html page
• for (i=0; i<15; i++)
  document.write ("Image " + i + " is " + document.images[i].src + "
  ");
• OR you can set up the array using Javascript
  imgarr=new Array(9);    // array of 9 elements
  imgarr[0]=new Image;   //new image
  imgarr[0].src="picnic02-1.jpg";
• OR use a loop to generate the pictures since they are similarly named
  imgarr=new Array(9);   
  for (i=0;i<8;i++){ imgarr[i]=new Image; imgarr[i].src="picnic02-"+(i+1)+".jpg"; }

Multidimensional Arrays

• Have to create an array of arrays. All dimensions start with 0.

  var table = new Array(10);
  for (var i =0; i < table.length; i++)
    table[i] = new Array(10);
  

• To access, use nested loops

  for (var row =0; row < table.length; row++)
    for (var col = 0; col < table[row].length; col++)
      table[row][col] = row *col;
  

• 10 rows: 0-9; 10 cols: 0-9;
• table[5][7] is 35

Array Methods

• join() - joins elements of an array into a string:

  var a=[1, 2, 3];
  a.join(); // returns "1,2,3"
  

• reverse() - reverses elements within the array

  var a=[1, 2, 3];
  a.reverse(); // array a now contains 3, 2, 1
  

• sort() - sorts elements of the array in place

  var a=[44, 2, 111, 6];
  a.sort(); // array a now contains 2, 6, 44, 111
  

• concat() - returns a new array

  var a=[44, 2, 111, 6];
  a.concat(4, 5) // returns 44, 2, 111,6, 4, 5
  

• slice()- returns a subarray of the specified elements

  var a=[44, 2, 111, 6];
  a.slice(1, 3) // returns 2, 111,6
  

• splice() - inserts or removes elements from an array

  var a=[1,2,3,4,5,6,7,8];
  a.splice(4) // returns [5,6,7,8]; a is [1,2,3,4]
  a.splice(1,2) // returns [1,2]; a is now [3,4]
  

• push(), pop() - adds and removes array elements from end of array
• unshift(), shift() -- adds to beginning of array

  var a=[];
  a.unshift (1); // a consists of [1], returns 1
  a.unshift (8); // a consists of [8, 1], returns 2 - length of array
  a.shift(); //a consists of [1], returns 8
  

• toString - converts array to a string '1,2,3'
• indexOf(), lastIndexOf() - search an array for a specified element

  a=[0,1,2,1,0];
  a.indexOf(1); // returns 1 - the index of the first one in a
  a.lastIndexOf(1); // returns 3 - the index of the last one in a