Q:

PHP order multiple RSS feeds by date

I have a bit of PHP code to merge two RSS feeds.  I was trying to sort the feeds by date, but I get the funny result that:

The two feeds get sorted separately (1st feed listed first, then
second feed)
The first feed gets sorted ascending and the second gets sorted descending. 

I want ALL of the data (feed 1 + 2 together) to be sorted by date with the latest item first.  Any help is much appreciated! 
This is my code (usort and foreach loop at the bottom):
<? php

class Feed_Miro
{
    public $urls = array();
    public $data = array();

    public function addFeeds( array $feeds )
    {
        $this->urls = array_merge( $this->urls, array_values($feeds) );
    }

    public function grabRss()
    {
        foreach ( $this->urls as $feed )
        {
            $data = @new SimpleXMLElement( $feed, 0, true );
            if ( ! $data )
                throw new Exception( 'Could not load: ' .  $feed );
            foreach ( $data->channel->item as $item )
            {
                $this->data[] = $item;
            }
        }
    }

    public function merge_feeds(){

        $temp = array();        
        foreach ( $this->data as $item )
        {
            if ( ! in_array($item->link, $this->links($temp)) )
            {
                $temp[] = $item;
            }
        }    $this->data = $temp;

    }

    private function links( array $items ){
        $links = array();
        foreach ( $items as $item )
        {
            $links[] = $item->link;
        }
        return $links;
    }
}

/********* 
add urls
*********/

$urls = array( 'http://www.voyagersfamily.ch/feed.xml', 'http://www.miroman.ch/feed.xml' );

try
{
    $feeds = new Feed_Miro;
    $feeds->addFeeds( $urls );
    $feeds->grabRss();
    $feeds->merge_feeds();
}
catch ( exception $e )
{
    die( $e->getMessage() );
}
// test from here
$data = array();
$data = $feeds -> data;

usort($data, function($a,$b){
    return $a->pubDate - $b->pubDate;
});

foreach ( $data as $item ) :
//foreach ( $feeds->data as $item ) :
extract( (array) $item );
? >
<div class="span4 profile">
<h3 class="profile-description"><a href="<?php echo $link; ? >" style="text-decoration:none;"><?php echo $title; ? ></a></h3>
<p class="profile-description"><?php echo $description; ? ><br>
published: <? php echo $pubDate; ? > <a href="<?php echo $link ? >" target="_blank">more</a></p>
</div>

<? php endforeach; ? >

A:

you are comparing strings , while you need to compare timestamps for example
this part:
usort($data, function($a,$b){
    return $a->pubDate - $b->pubDate;
});

needs to be converted into timestamps and compare as following :
usort($data, function($a,$b){
    return strtotime($a->pubDate) - strtotime($b->pubDate);
});

for example :
$arr = [
    ['pubDate' => 'Wed, 07 Nov 2012 10:15:00 GMT',],
    ['pubDate' => 'Thu, 23 Feb 2017 09:00:00 GMT', ],
    ['pubDate' => 'Mon, 30 May 2016 10:00:00 GMT', ]
];

usort($arr, function($a, $b) {
    return strtotime($a['pubDate']) > strtotime($b['pubDate']);
});

print_r($arr);

this will return as :
Array (
    [0] => Array (
        [pubDate] => Wed, 07 Nov 2012 10:15:00 GMT
    )
    [1] => Array (
        [pubDate] => Mon, 30 May 2016 10:00:00 GMT
    )
    [2] => Array (
        [pubDate] => Thu, 23 Feb 2017 09:00:00 GMT
    )
)

while sorting the array without converting into timestamps will not sort it

