sorting arrays using object vars

Anon

Hi there,

I've got a problem in that I'm trying to sort an array of objects(each of which contains a number of variables), using the variables within each object.

I'm sure there must be a short method to do this and keep the associativity between the object parameters, but I can't find anything anywhere! I've tried using all the sort commands listed on php.net, but all to no avail!

Help! I've been trying to figure this out for ages......

Cheers,

Ian

Anon

Hi, Ian!

I've already posted a thread in response to another similar question. What you need to do is find PHP sorting algorithm implementations like quicksort, shellsort, bubblesort - on planetsourcecode.com, for instance. Each of them have their own tradeoffs, for instance quicksort is very effective for almost sorted arrays.
After that you need to create a comparison function which will compare two objects. You may extend this function so that it could sort objects by any member variable.

It can look like this
function compare_obj($obj1, $obj2, $var)
{
if ($obj1->$var == $obj2->$var) return 0;
return ($obj1->$var < $obj2->$var ? -1 : 1);
}

Then, in the sorting function, just replace the standard comparison function with this one. The $var can be put as the last parameter to the sorting function itself and then passed to the comparison function so you could sort by any member variable.

Hope this helps,
Stas

Anon

Hi again,

Got this "Sort of", working now. Just wondering how I supply the variable $var when I call the function using the folowing method:

uasort($articles, compare_obj);

It doesn't seem to like it when I supply the argument within compare_obj($obj1,$obj2,author) for instance?

what are $obj1 and $obj2 parsed to the function compare_obj as??

Cheers, Thanks again,

Ian

Anon

Hi again, Ian!

You should leave the comparison function alone since you're using uasort which requires that the comparison function has only 2 arguments. In the comparison function itself, use this:

$obj_comp_var = 'author';

function cmp (&$a, &$b) {

global $obj_comp_var;
if ($a->$obj_comp_var == $b->$obj_comp_var) return 0;
return ($a->$obj_comp_var > $b->$obj_comp_var) ? -1 : 1;
}

With objects, it's always better to pass them by reference, hence I am using &$a instead of $a in the function's declaration.

My first example was for such a case when you implement both functions (comparison and sorting) yourself. I think I've overlooked uasort and usort.

I hope this helps,
Stas

Anon

Cheers,

You helped loads....

I should of thought of the global variables thing.....what a ditz I am!

Ian

Anon

Hi, Ian!

Glad I could help.
Thanks to you for noticing uasort().

Best regards,
Stas