Sorting Post Titles without Articles

Hi,

You can achieve this with a bit of custom code to support your use. You will need to add something similar to the following into your theme of child-theme’s functions.php (I hope I’ve written it correctly, but do test it first if you can, because I’m not certain it’s perfect):

function ignore_articles_in_az_index( $indices, $item ) {
    // all the articles we want to strip
    $articles = array( 'a', 'an', 'the' );

    // save the title for quicker access
    $title = $item->post_title;

    foreach( $article in $articles ) {
        // get the length of the 'article'
        $len =  mb_strlen( $article );

        //check whether this 'article' starts the title (+1 added to length to 
        //include space to ensure we don't match partial words like 'another'
        //would match 'an', but won't match 'an ')
        if ( mb_substr( $title, 0, $len + 1, 'UTF-8' ) === $article . ' ' ) {
            //get the true first letter to index by after the 'article'
            $index = mb_substr( $title, $len, $len + 1 );
            //return the new index - this is needlessly complex, I'll fix it one day
            return array(
                $index => array( array(
                    'title' => $title,
                    'item' => $item,
                ) ),
            );
        }
    }

    //if we get here then we didn't change the index letter so we return the
    //unmodified original to not break anything
    return $indices;
}

//hook the correct plugin-provided filter
add_filter( 'a_z_listing_item_indices', 'ignore_articles_in_az_index', 10, 2 );

References:
https://developer.ww.wp.xz.cn/reference/functions/add_filter/
https://secure.php.net/manual/en/function.mb-strlen.php
https://secure.php.net/manual/en/function.mb-substr.php
https://a-z-listing.com/reference/hooks/a_z_listing_item_indices/