Alphabetize Wordpress taxonomy list by last name

Question

I have a query which outputs a list of taxonomy tags, organised by FIRST NAME with an alphabetical heading, like so:

E

Elena Ferrante 

H

Helen DeWitt

J

Joan Didion

Jonathan Franzen 

K

Kazuo Ishiguro

M

Maggie Nelson

P

Plato

R

Rachel Cusk

Roberto Bolaño

S

Sheila Heti

etc.

---

How can I alphabetize this list of taxonomy tags by LAST NAME instead of FIRST NAME? So the result would be:

B

Roberto Bolaño

C

Rachel Cusk

D

Helen DeWitt

Joan Didion

F

Elena Ferrante

Jonathan Franzen 

H

Sheila Heti 

I

Kazuo Ishiguro

P

Plato

N

Maggie Nelson

etc.

---

Here is the query:

    <?php       
    $list = '';
    $groups = array();
    $tags = get_terms('authors',$args);
    if( $tags && is_array( $tags ) ) {
        foreach( $tags as $tag ) {
            $first_letter = strtoupper( $tag->name[0] );
            $groups[ $first_letter ][] = $tag;
        }
        if( !empty( $groups ) ) {
            foreach( $groups as $letter => $tags ) {
                $list .= "<div class='titleLetter'>" . $letter . "</div><ul>";
                foreach( $tags as $tag ) {
                    $list .= '<li><a href="/authors/'.$tag->slug.'">'.$tag->name.'</a></li>';
                }
                $list .= '<br></ul>';
            }
            $list .= '';
        }
    }
    echo $list;  ?>

Answer 1

If the given code works for First Name ordering. Then this one will work for orderby lastname.

<?php       
$list = '';
$groups = array();
$tags = get_terms('authors',$args);
if( $tags && is_array( $tags ) ) {
    $i=0;
    foreach( $tags as $tag ) {
        $lastname_arr=explode(' ', $tag->name);
        $lastname=$lastname_arr[count($lastname_arr)-1];
        $first_letter = strtoupper( $lastname[0] );
        $groups[ $first_letter ][$lastname.'_'.$i] = $tag;
        $i++;
    }
    foreach($groups as $key=>$group ){
        ksort($groups[$key]);
    }
    ksort($groups);
    if( !empty( $groups ) ) {
        foreach( $groups as $letter => $tags ) {
            $list .= "<div class='titleLetter'>" . $letter . "</div><ul>";
            foreach( $tags as $tag ) {
                $list .= '<li><a href="/authors/'.$tag->slug.'">'.$tag->name.'</a></li>';
            }
            $list .= '<br></ul>';
        }
        $list .= '';
    }
}
echo $list;  
?>

What i did here are:

• replaced array index with the first letters of lastnames.
• applied ksort(sort by key) function to array and sub-arrays (in order to create custom orderby on new indexes)