PHP：按多个元素对XML节点列表进行排序

Question

Beginner programmer here.

I am in php, working with a dom document nodelist comprising of selected nodes retrieved from an XPath query on an xml file. Excerpt of contents of nodelist:

<properties>
    <property>
        <price>270</price>
        <address>3/2 Farran Street, Castlemaine, VIC, Australia</address>
        <infants>3</infants>
    </property>
    <property>
        <price>250</price>
        <address>2/37 William Street, Castlemaine, VIC, Australia</address>
        <infants>2</infants>
    </property>
    <property>
        <price>250</price>
        <address>2/37 William Street, Castlemaine, VIC, Australia</address>
        <infants>3</infants>
    </property>
    ...

I wish to sort the nodelist by price ascending, and in the case of matching prices, by no of infants descending. In the above snippet, for example, the result would be:

<property>
    <price>250</price>
    <address>2/37 William Street, Castlemaine, VIC, Australia</address>
    <infants>3</infants>
</property>
<property>
    <price>250</price>
    <address>2/37 William Street, Castlemaine, VIC, Australia</address>
    <infants>2</infants>
</property>
<property>
    <price>270</price>
    <address>3/2 Farran Street, Castlemaine, VIC, Australia</address>
    <infants>3</infants>
</property>

I have seen some sorting questions answered relating to multi-dimensional arrays but I can't seem to translate these to nodelists. I can sort by price ok (see below), but I can't determine how to then sort by infants.

$properties = iterator_to_array($matches); // where matches = a return from an XPath query
usort($properties, 'sortByPrice');

function sortByPrice ($a, $b) {
    $aPrice = $a->getElementsByTagName("price");
    $aPrice = $aPrice->item(0)->nodeValue;
    $bPrice = $b->getElementsByTagName("price");
    $bPrice = $bPrice->item(0)->nodeValue;
    return (int) $aPrice - (int) $bPrice;
}

Answer 1

if your code works ok for price, why not just extend it:

$properties = iterator_to_array($matches); // where matches = a return from an XPath query
usort($properties, 'sortByPrice');

function sortByPrice ($a, $b) {
    $aPrice = $a->getElementsByTagName("price");
    $aPrice = $aPrice->item(0)->nodeValue;
    $bPrice = $b->getElementsByTagName("price");
    $bPrice = $bPrice->item(0)->nodeValue;
    $r = (int) $aPrice - (int) $bPrice;
    if (!$r) {
       $ainfants = $a->getElementsByTagName("infants");
       $ainfants = $ainfants->item(0)->nodeValue;
       $binfants = $b->getElementsByTagName("infants");
       $binfants = $bPrice->item(0)->nodeValue;
       $r = (int) $ainfants - (int) $binfants;
    }
    return $r;
}