Sorting an associative array on one element

[redneck]

I am working with an associative array called $posts. I would like to sort $posts before I start doing some work on the contents of the array. One of the elements of the array is $posts['post_title'].

What syntax would I use to sort the array on the elements in $posts['post_title']?

[Weedpacket]

I think perhaps [man]array_multisort[/man] will do the job, but it may be a bit complicated to use. There is also [man]usort[/man], where you write a function that specifies how to compare array elements.

[redneck]

Thanks. I saw those in the PHP Cookbook.

But the explanations confuse me.

I am not sure where, for example, I define the key on which the sort is performed.

All I'm starting with is an associative array. I just want to run a sort on the lements of the array, using just one of the keys.

Sometimes I'm pretty dim.

[swr]

I am not sure where, for example, I define the key on which the sort is performed.

In the comparison function.

function compare_by_post_title($a, $b) {
    return strcmp($a['post_title'], $b['post_title']);
}

usort($posts, 'compare_by_post_title');

[edit]
I'm assuming $posts is an array of associative arrays. From your previous comment it looks like that is not the case. What is $posts['post_title'] ?
[/edit]

[redneck]

Originally posted by swr
I'm assuming $posts is an array of associative arrays. From your previous comment it looks like that is not the case. What is $posts['post_title'] ?
[/B]

$posts is an associative array. $posts['post_title'] would be a text string.

My confusion is simply that I am not sure where name the key on which the sort is to be performed when calling the function (I think I understand how the user-defined compare funtion works). The examples assume much more complex problems than the one I am trying to solve.

[swr]

Originally posted by redneck
$posts is an associative array. $posts['post_title'] would be a text string.

I don't understand... You have a single associative array, with a single title. What is it you are trying to sort?

You do realize that when you only have a single item it never requires sorting, right? :p

[redneck]

Originally posted by swr
I don't understand... You have a single associative array, with a single title. What is it you are trying to sort?

The elements of the array.

Here's what the array looks like:

print_r($posts):

Array
(
    [0] => stdClass Object
        (
            [ID] => 6
            [post_author] => 1
            [post_date] => 2004-03-02 08:43:17
            [post_content] => I think where I\'m headed is toward the 
            [post_title] => Shower thoughts
            [post_category] => 0
            [post_excerpt] => 
            [post_lat] => 
            [post_lon] => 
            [post_status] => publish
            [comment_status] => open
            [ping_status] => open
            [post_password] => 
            [post_name] => shower-thoughts
            [to_ping] => 
            [pinged] => 
            [post_modified] => 0000-00-00 00:00:00
            [post_content_filtered] => 
            [rel_id] => 8
            [post_id] => 6
            [category_id] => 1
        )

[1] => stdClass Object
    (
        [ID] => 5
        [post_author] => 1
        [post_date] => 2004-03-01 07:17:52
        [post_content] => I think my two-year search for 
        [post_title] => a savage journey into the heart of the American dream
        [post_category] => 0
        [post_excerpt] => 
        [post_lat] => 
        [post_lon] => 
        [post_status] => publish
        [comment_status] => open
        [ping_status] => open
        [post_password] => 
        [post_name] => a-savage-journey-into-the-heart-of-the-american-dream
        [to_ping] => 
        [pinged] => 
        [post_modified] => 0000-00-00 00:00:00
        [post_content_filtered] => 
        [rel_id] => 6
        [post_id] => 5
        [category_id] => 1
    )

)

I want the elements of the array sorted on one of the keys (['post_title'], but it could be any of them).

I apologize, since I'm sure it is very easy and I'm just not describing it well.

[swr]

No associative array there. What you have is an array of objects, which is probably the best form for the data. There is no "$posts['post_title']" but there is "$posts[0]->post_title" and "$posts[1]->post_title". Be sure to understand the structure of your data; it's a very important detail if you want your code to actually work.

Did you get this as the result of a SQL query? If so, just add "order by post_title" to get what you want.

If not, a slight change to the code I posted earlier to make it work with an array of objects instead of an array of associative arrays:

function compare_by_post_title($a, $b) {
    return strcmp($a->post_title, $b->post_title);
}

usort($posts, 'compare_by_post_title');

[redneck]

No, I would rather do the sort as a PHP function than in the SQL call.

Thank you for bringing the array structure to my attention (obviously, I am hacking something someone else built). I never actually tried any of the other examples since I wanted to understand them first. I guess it was fortunate that I actually posted the array structure, otherwise I would have been complete confused as I started hacking away, getting all kinds of variable mismatch errors.

I think the function you proposed will work very nicely (and, yes, I think I understand it now).