Javascript sort string or number

Question

EDIT: Pete provided a really good solution that works when the fields contain numbers, however I need to be able to sort strings too - any ideas?

I'm trying to write a javascript sorting algorithm that will sort a table based on the column clicked - I know this is semi-reinventing the wheel but the design is too complex for me to try and insert some other plugin etc.

Some columns are text, some columns are numbers.

Clicking a column calls: sort(X,Y). X is the column number so we know which cells to compare for the sort. Y is the mode, i.e. ascending or descending.

The code for the sort function is:

function sort(field, mode) {
var tabrows = 0;
$(".data tr").each(function() { if($(this).hasClass("hdr")) { } else {tabrows++;} });   
var swapped;
do {
        swapped = false;
        for (var i=0;i< tabrows; i++) {

            var j = i + 3;
            var k = i + 4;  

            var row1 = $(".data tr:nth-child("+j+")");
            var row2 = $(".data tr:nth-child("+k+")");

            var field1 = row1.find("td:eq("+field+")").text();      
            var field2 = row2.find("td:eq("+field+")").text();

            if(shouldswap(field1, field2, mode)) {
                swaprows(row1, row2);
                swapped = true;
            }
        }
    } while (swapped);
}

The shouldswap function is as follows:

function shouldswap(field1, field2,mode) {


    if(field1 > field2) {
            if(mode==1) {   
                return true;
            } else {
                return false;
            }   
    }

    return false;

}

Code for swaprows function:

function swaprows(row1, row2) {
      row2.insertBefore(row1);
}

Can anyone see why this would cause the browser to freeze/lockup. I've been working on this for quite a while so I think a fresh pair of eyes may point out something silly! Any help is appreciated :)

Can you post the code to swaprows? Perhaps there's a problem with the actual swapping of rows, causing it to never be able to finish sorting? — Clay Garrett
– Clay Garrett, Commented Sep 12, 2012 at 16:23
Did you test your code with a large or small amount of rows? — MaxArt
– MaxArt, Commented Sep 12, 2012 at 16:32
Considered to put your data in an array and use the more efficient sort method of Arrays? — some
– some, Commented Sep 12, 2012 at 16:37
Just curious when you say, "the design is too complex to insert a plugin." Something like jqGrid has all this functionality AND it has a feature where it can be retrofitted to an already existing table (since it seems like you already have that). Not that you shouldn't figure out your problem, but there may be other alternatives. — JasCav
– JasCav, Commented Sep 12, 2012 at 16:55

Pete · Accepted Answer · 2012-09-13 15:06:34Z

2

The problem might be that you're calling the jQuery constructor a bunch of times and doing heavy operations on it (e.g. using .find() with complex selectors). Therefore, your function is just slow and that's probably the issue.

The good news is that JavaScript has a native implementation of QuickSort (a very fast sorting function) that will probably take care of your needs. When combined with a reduction in expensive calls, your code should end up being enormously more efficient. I'd change your code to look like this:

var sortByField = function(field, mode) {
    var numExp = /^-?\d*\.?\d+$/;
    var $rows = $(".data tr:not(.hdr)"), $table = $(".data");
    $rows.each(function () {
        this.fieldVal = $(this).find("td:eq("+field+")").text();
        if(numExp.test(this.fieldVal)) { //if field is numeric, convert it to a number
            this.fieldVal = +this.fieldVal;
        }
    }).sort(function (a, b) {
        if (mode === 1) {
            return (a.fieldVal > b.fieldVal) ? -1 : 1;    
        }    
        return (a.fieldVal < b.fieldVal) ? -1 : 1;
    }).detach().each(function () {
        $(this).appendTo($table);
    });
};

This won't work well with multiple tables on one page (because it assumes everything is on the same table). So if you want to do that, you should pass in the table or table selector as a parameter. But that's an easy fix to make. You can see my solution in action here:

http://jsfiddle.net/r8wtK/ (updated)

It should be far more efficient than your code and should reduce "freezing" by quite a bit (ore even entirely).

UPDATE:

The OP noted that some fields may contain strings. Doing a string comparison on numbers is bad because it returns a lexicographical ordering (e.g. "10" < "2"). So I added a test to see if the data appear to be numeric before doing the sort.

edited Sep 13, 2012 at 15:06

answered Sep 12, 2012 at 16:51

Pete

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4 Comments

Dave Clarke Over a year ago

Hi - This looks really promising but just a quick question! Some of the columns contain strings, e.g 'Finished' or 'Active' that I need to be able to sort still. I notice one of your lines forces it to be a number - will this prevent the functionality I want? Cheers, Dave.

Pete Over a year ago

@swiss196 Let me update to show how to do that. It's simple but requires a couple edits.

Pete Over a year ago

@swiss196 Updated. Drop another comment if you spot any issues. Make sure to check out the updated JSFiddle demo. One small note, this will fail if you mix numbers and strings in a column. If that's a requirement, I'll leave it as a challenge to you! :-) (hint: the best approach may be to use classes to define columns as strings or numbers for the purposes of sorting)

IcedQuick Over a year ago

I was looking for one button that would do the work of the two sets of buttons for each column in the above fiddle. I've expanded the click function to toggle the data-mode of any buttons, so clicking it again gives the sort in reverse: ` var a = $(this).data('mode'); console.log("a is " + a); if( typeof a !== 'undefined' ) { if (a == "0") { $(this).data('mode',1); console.log("now a is " + $(this).data('mode')); } if (a == "1") { $(this).data('mode',0); console.log("now a is " + $(this).data('mode')); } } `

Clay Garrett · Accepted Answer · 2012-09-12 16:44:24Z

0

Could it be that you're adding 3 and 4 to i in order to get your row indices? So when i gets to (tabrows-1), it appears that it will be trying to access rows with index of (tabrows+2) and (tabrows+3). If I understand your logic correctly, these are out of bounds, so row1, row2, field1 and field2 will be empty. Therefore, if you're in mode==1, I think this will make it so that your algorithm attempts to swap these two non-existent rows and keeps comparing for infinity. Does this make sense, or am I misunderstanding your logic?

If that's the case, I think you just need to change your for loop to:

for (var i=0;i< tabrows-4; i++) {
     // your code
}

What is the purpose of adding 3 to j and 4 to k anyway? Do you have 3 rows of data at the top that you don't want to compare?

answered Sep 12, 2012 at 16:44

Clay Garrett

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1 Comment

Dave Clarke Over a year ago

Thanks for you're input. You're halfway right, there are two rows of data (header rows) that I don't want to sort & nth-child selector is not zero indexed, it starts at 1.

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