array.html
///////////////////
array.js
function example1(){
// create new arrays
var a = [];
var sparse = [0, 1.1, , true, , "x", , {z:4, r:7}]; // creates sparse array
var empty = new Array(); // creates empty array
var array = new Array(5); // single argument, represents length
var array2 = new Array(1, 2, 3, 4, 5); // [1 2 3 4 5]
console.log(sparse[6]); // undefined
console.log(sparse[-1]); // undefined, "-1" treated as object property
// not as array index, which is non-existent
console.log(sparse.length); // 8
console.log(empty.length); // 0
console.log(a.length); // 0
console.log(array.length); // 5
console.log(array2.length); // 5
}
function example2(){
var array = [1,2,3,4,5]
// Read and write to arrays
console.log("---------------");
array[5] = 6; // [1 2 3 4 5 6]
console.log(array.length); // 6
array["10"] = 11; // set element at index 10 with value 11
// "10" behaves like array index and not as object
// property
console.log(array.length); // length = 11, only 7 elements in array
// sparse arrays
console.log("----------");
var a = new Array(5); // length 5 and no elements
var a1 = [,,]; // length = 2 with no elements
var a2 = [undefined,,]; // length = 2 with 1 undefined element
console.log(a1.length); // 2
console.log(a2.length); // 2
console.log(0 in a1); // false, a1 has no element at 0
console.log(0 in a2); // true, a2 has element undefined at 0
// array.length
var b = [1,2,3,4,5]; // [1,2,3,4,5]
b.length = 3; // [1,2,3]
b.length = 0; // delete all elements
b.length = 5; // length = 5, no elements
// add and delete elements from an array
console.log("-----------------");
var c = [];
c.push(1,2,3);
console.log(c); // [1, 2, 3]
delete c[1];
console.log(c) // [1, , 3] sparse array
console.log(1 in c); // false
console.log(c.length); // 3
}
function example3(){
var a = [1,2,3,4,5]; // non-sparse
var array = [1,null,3,undefined,5, , 7, null, , 8]; // sparse array
var i; // index variable
console.log("---------------");
for (i in a) // printing non-sparse array
console.log(a[i]);
console.log("---------------");
for(i = 0; i < array.length; i++){ // looping sparse array
if(!array[i]) continue; // skip nulls, undefined and non-existent
console.log(array[i]);
}
// Multidimensional array
console.log("--------------");
var table = new Array(5); // 5 rows
for(i = 0; i < table.length; i++)
table[i] = new Array(5); // 5 columns
for(var row = 0; row < table.length; row++){
for(var col = 0; col < table[row].length; col++){
table[row][col] = row * col;
}
}
console.log(table[2][3]); // 6
}
function example4(){
// join, converts elements to strings,concatenates, returns string
var a = [1,2,3,4,5];
console.log(a.join())
console.log("-----------------")
// reverse, reverses elements of array and returns reversed array
// modifies array
console.log(a.reverse())
console.log("----------------")
// sort(), sorts elements in alphabetical order, case-sensitive
// modifies array
// sort(), sorts non-alphabetically
// comparison function: decides on 2 element comparison
// if first > second, return > 0
// if first < second, return < 0
// if first == second, return 0
var fruits = ["apple", "orange", "Banana"];
console.log(fruits.sort());
console.log(fruits.sort(function(s, t){
var a = s.toLowerCase();
var b = t.toLowerCase();
if (a < b) return -1;
if (a > b) return 1;
return 0;
}))
// concat, returns new array with concatenated elements
// returns new concatenated array
var x = [1,2,3]; // [1,2,3]
var y = x.concat([4,5,[6,7]]); // [1,2,3,4,5,[6,7]]
console.log("-------------");
// slice(x,y), returns subarray [x,y), does not modify array
// x : start index, inclusive
// y : end index, exclusive
// index:[ 0, 1, 2, 3, 4]
// index:[-5, -4, -3, -2, -1]
var z = [ 1, 2, 3, 4, 5];
console.log(z.slice(0,3)); // [1,2,3]
console.log(z.slice(3)); // [4,5]
console.log(z.slice(1,-1)); // [2,3,4]
console.log(z.slice(-3,-2)); // [3]
console.log("------------------------");
// splice(x,y), x:deleting index, y:number of elements to delete
// modifies the array, moves elements over to the left
var f = [1,2,3,4,5,6,7,8];
console.log(f.splice(4)); // Returns [5,6,7,8], f is [1,2,3,4]
console.log(f.splice(1,2)); // Returns [2,3], f is [1,4]
console.log(f.splice(1,1)); // Returns [4], f is [1]
// push()->append at the end of array
// pop()->deletes at the end of array
// modify the array in place
var stack = [];
stack.push(1,2) // [1,2]
stack.pop(); // [1]
stack.push(3); // [1,3]
stack.pop(); // [1]
stack.push([4,5]) // [1,[4,5]]
stack.pop(); // [1]
stack.pop(); // []
// shift->delete at the beginning, shifts elements to the left
// unshift->insert at the beginning, shifts elements to the right
var h = [];
h.unshift(1); // [1]
h.unshift(2); // [2,1]
h.shift(); // [1]
h.unshift(3,[4,5]); // [3,[4,5],1]
h.shift(); // [[4,5],1]
h.shift(); // [1]
h.shift(); // []
// toString()->returns string with array elements
console.log("--------------------");
console.log([1,2,3].toString()); // '1,2,3'
console.log([1,[2,'c']].toString()); // '1,2,c'
console.log("--------------");
// indexOf()->returns the index for the first occurrence of an element
// lastIndexOf()->returns the index for last occurrence of an element
var g = [0,3,2,0,1,2,3,5,6,3];
console.log(g.indexOf(5)); // 7
console.log(g.lastIndexOf(3)); // 9
/////////////////////////////////////////
console.log("---Array methods----");
// forEach, map, filter, every, some, reduce, reduceRight
// First argument is a function and invoke that function once for each
// element of the array
// function takes 3 arguments:
// 1st is the value of each element in array
// 2nd, is the value of this keyword,
// 3rd is return value
//////////////////////////////////////////
// forEach
var array = [1,2,3,4,5];
var sum = 0;
array.forEach(function(value) {sum += value});
console.log(sum); // 15
// map
var m = array.map(function(x) {return x * x});
console.log(m) // [1,4,9,16,25]
// filter
var smallerthan3 = array.filter(function(x) { return x < 3 });
console.log(smallerthan3); // [1,2]
// every and some, returns true or false
console.log(array.every(function(x) {return x < 10})); // true, all <10
console.log(array.some(function(x) { return x%2 === 0 })); // true, some even
// reduce->combine elements and produce single value
// reduce(previousValue,currentValue,index,array), initial value(optional)
console.log([0,1,2,3,4,5].reduce(function(x,y) {return x+y}, 0)) // 15=0+15
// reduceRight(previousValue, currentValue, index, array), initial value (optional)
console.log([0,1,2,3,4].reduceRight(function(x,y) {return x+y}))
// previousValue = 4, currentValue = 3, index = 3
// previousValue = 7, currentValue = 9, index = 2
// previousValue = 9, currentValue = 1, index = 1
// previousValue = 10,currentValue = 0, index = 0
// Return 10
console.log([0,1,2,3,4].reduceRight(function(x,y) {return x+y}, 10));
// previousValue = 10, currentValue = 4, index = 4
// previousValue = 14, currentValue = 3, index = 3
// previousValue = 17, currentValue = 2, index = 2
// previousValue = 19, currentValue = 1, index = 1
// previousValue = 20,currentValue = 0, index = 0
// Return 20
}