<> Chapter 6 Arrays 2016.12.24

Array Literals#

var empty = []; 
var numbers = ['zero', 'one', 'two', 'three', 'four', 'five', 'six', 'seven', 'eight', 'nine' ];

empty[1] // undefined
numbers[1] // 'one'
empty.length // 0
numbers.length // 10

var misc = ['string', 98.6, true, false, null, undefined, ['nested', 'array'], {object: true}, NaN, Infinity]; 
misc.length // 10

Length#

var myArray = []; 
myArray.length // 0

myArray[1000000] = true; 
myArray.length // 1000001 
// myArray contains one property.

Delete#

delete numbers[2]; // numbers is ['zero', 'one', undefined, 'shi', 'go']

numbers.splice(2, 1); // numbers is ['zero', 'one', 'shi', 'go']

Enumeration#

var i; 
for (i = 0; i < myArray.length; i += 1) {
  document.writeln(myArray[i]); 
}

Confusion#

var is_array = function (value) { 
  return value && typeof value === 'object' && value.constructor === Array;
};

var is_array = function (value) { 
  return Object.prototype.toString.apply(value) === '[object Array]';
};

Methods#

Array.method('reduce', function (f, value) { 
  var i;
  for (i = 0; i < this.length; i += 1) { 
    value = f(this[i], value);
  }
  return value; 
});

// Create an array of numbers.
var data = [4, 8, 15, 16, 23, 42];
// Define two simple functions. One will add two 
// numbers. The other will multiply two numbers.
var add = function (a, b) { 
  return a + b;
};
var mult = function (a, b) { 
  return a * b;
};
// Invoke the data's reduce method, passing in the 
// add function.
var sum = data.reduce(add, 0); // sum is 108
// Invoke the reduce method again, this time passing 
// in the multiply function.
var product = data.reduce(mult, 1); // product is 7418880

// Give the data array a total function.
data.total = function () {
  return this.reduce(add, 0);
};
total = data.total(); // total is 108

Dimensions#

Array.dim = function (dimension, initial) { 
  var a = [], i;
  for (i = 0; i < dimension; i += 1) { 
    a[i] = initial;
  }
  return a;
};
// Make an array containing 10 zeros. 
var myArray = Array.dim(10, 0);

for (i = 0; i < n; i += 1) {
  my_array[i] = [];
}
  // Note: Array.dim(n, []) will not work here.  
  // Each element would get a reference to the same  
  // array, which would be very bad.

Array.matrix = function (m, n, initial) { 
  var a, i, j, mat = []; 
  for (i = 0; i < m; i += 1) {
    a = []; 
    for (j = 0; j < n; j += 1) {
      a[j] = initial; 
    }
    mat[i] = a;
  }
  return mat;
};
// Make a 4 * 4 matrix filled with zeros.
var myMatrix = Array.matrix(4, 4, 0);
document.writeln(myMatrix[3][3]); // 0

// Method to make an identity matrix.
Array.identity = function (n) { 
  var i, mat = Array.matrix(n, n, 0); 
  for (i = 0; i < n; i += 1) {
    mat[i][i] = 1; 
  }
  return mat;
};
myMatrix = Array.identity(4);
document.writeln(myMatrix[3][3]); // 1