Question

0

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:

ADSL Router: 192.168.0.1
Network Switch: 192.168.0.2
Gary's Mac: 192.168.0.15
Production Email: 192.168.0.60

flag	asked Jun 25 at 18:42 Gary Willoughby 3,075●5●30

	You should use the array literal syntax `[ … ]` and not `new Array()`. – Gumbo Jun 25 at 18:56
	why ? – Gary Willoughby Jun 26 at 18:49

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Ken Egozi · Accepted Answer · 6/25/2009 6:51:39 PM UTC

5

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

answered Jun 25 at 18:51

Ken Egozi
227●6

	Talk about 'can't see the wood for the trees'! Thanks. – Gary Willoughby Jun 25 at 18:54
	You're welcome :) Happens to me each and every day at work – Ken Egozi Jun 25 at 19:47

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Gumbo · Answer 2 · 6/25/2009 6:50:36 PM UTC

5

You’re comparing the wrong values. Try this:

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

answered Jun 25 at 18:50

Gumbo
21.3k●12●39

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Peter Bailey · Answer 3 · 6/25/2009 6:50:37 PM UTC

1

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;
}

answered Jun 25 at 18:50

Peter Bailey
7,893●1●5●21

	@Peter: return a[1][3] - b[1][3] will return 0 if they are the same. There is a potential for overflow when using 'a - b', but since he is sorting the last value of an IP address, we know that the value will never result in an overflow. – Grant Wagner Jun 25 at 18:56
	Yeah, I sorta figured it out after I posted. I'll leave this as it is, though, as an explicit method for doing the sort. – Peter Bailey Jun 25 at 19:05

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mkoryak · Answer 4 · 6/25/2009 6:53:41 PM UTC

1

change your sort function to:

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

answered Jun 25 at 18:53

mkoryak
1,866●2●17

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Christoph · Answer 5 · 6/25/2009 7:20:51 PM UTC

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]; });

Creating a custom array within an array sort function in Javascript.

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