Creating a custom array within an array sort function in Javascript

Question

What would i need to put in the SortIP function to make the custom sort function sort the array by the last digit of the IP number. This doesn't work.

function SortIP(a, b)
{
    return a[0][3] - b[0][3];
}

LAN = new Array
(
    ["ADSL Router", [192, 168, 0, 1]],
    ["Gary's Mac", [192, 168, 0, 15]],
    ["Network Switch", [192, 168, 0, 2]],
    ["Production Email", [192, 168, 0, 60]]
);
LAN.sort(SortIP);

expected array order:

1. ADSL Router: 192.168.0.1
2. Network Switch: 192.168.0.2
3. Gary's Mac: 192.168.0.15
4. Production Email: 192.168.0.60

Answer 1

You're almost there

just replace

return a[0][3] - b[0][3];

with

return a[1][3] - b[1][3];

and you're done.

Why? Because the IP is the second (Index=1) cell of each array.

Answer 2

You’re comparing the wrong values. Try this:

function SortIP(a, b) {
    return a[1][3] - b[1][3];
}

Answer 3

The values sent to the sort handler are values of the array being sorted.

Since this is a bubble sort, you have to return 0 if the items are the same, 1 if a > b, and -1 if b > a;

function SortIP(a, b)
{
    if ( a[1][3] == b[1][3] ) return 0;
    return ( a[1][3] > b[1][3] ) ? 1 : -1;
}

Answer 4

change your sort function to:

function SortIP(a, b)
{
    return a[1][3] - b[1][3];
}

Answer 5

If you want to sort by the complete address, it might be a good idea to write a thin wrapper for the array containing the bytes:

function IP4() {
    var ip = Array.prototype.slice.call(arguments, 0, 4);
    ip.toString = IP4.toString;
    ip.valueOf = IP4.valueOf;
    return ip;
}

IP4.toString = function() {
    return this.join('.');
};

IP4.valueOf = function() {
    return (this[0] << 24) | (this[1] << 16) | (this[2] << 8) | this[3];
};

var LAN = [
    ["ADSL Router", IP4(192, 168, 0, 1)],
    ["Gary's Mac", IP4(192, 168, 0, 15)],
    ["Network Switch", IP4(192, 168, 0, 2)],
    ["Production Email", IP4(192, 168, 0, 60)]
];

LAN.sort(function(a, b) { return a[1] - b[1]; });