Sorting

With JSON data and JS arrays, dorting based on a particular key becomes an useful operation. In this section we discuss the basics of sorting by looking at bubbule sort as a standard sorting algorithm.

Bubble Sort

Bubble Sort is a sorting algorithm that sorts the array two members at a time. The idea of bubble sort is simple -- look at two adjacent elements in the array; are they sorted?. If already sorted then do nothing; if unsorted swap the position of the 2 elements.

How many passes (iterations) of the array is needed? -- no more than the size of the array. Let us look at sorting an array [6,5,3,1,8,7,2,4]

var arr = [6,5,3,1,8,7,2,4];
for (var i = 0; i < arr.length; i++){
  for (var j = 0; j < arr.length -i; j++){
    if(arr[j]>arr[j+1]){
      var temp = arr[j];
      arr[j] = arr[j+1];
      arr[j+1] = temp;
    }
  }
}

console.log(arr);

This process is visualized below [Ref.]:

Other Sorting Algorithms

Bubble Sort is just one of the many different sorting algorithms. The similarity between all these is that they all employ the sorting operator. They differ in only how they traverse and iterate over arrays. Therefore the key to any sorting is the comparison operator.

Sorting JS Arrays

JS array has a built in sort() method. An array can be sorted like so:

var arr = [6,5,3,1,8,7,2,4];
arr.sort();

The above invocation of sort() uses the default sorting function function(a,b){ return a > b }, and is equivalent to:

arr.sort(function(a,b){ return a > b });

To sort the array in decending order we reverse the sorting function.

arr.sort(function(a,b){ return a < b });

Since the built-in sort() method of Arrays, allows us to customize the sorting operator we can now sort Arrays of object based on any key.

var arr = [
{fname:"John",
 lname:"Smith"},
{fname:"Jane",
 lname:"Dow"},
{fname:"Alice",
 lname:"Hernandez"},
{fname:"Bob",
 lname:"Patel"},
{fname:"Rob",
 lname:"Grande"},
{fname:"Sally",
 lname:"Mendez"}
];

// sort by first name (alphabetical order)
arr.sort(function(a,b){return a.fname > b.fname});

// sort by first name (reverse alphabetical order)
arr.sort(function(a,b){return a.fname < b.fname});