bp-sort-members-by-last-name.php

<?php
// Sort BuddyPress users by last name
//
// Use this Gist to sort members alphabetically by last name in the
// members directory. Follow the instructions below and drop the code
// in your functions.php or your functions plugin.
//
// Updated to work with BP 1.7. See earlier revisions of this gist for
// earlier versions of BP.

/**
 * Sort users by last name
 *
 * Changes the querystring for the member directory to sort users by their last name
 *
 * @param BP_User_Query $bp_user_query
 */
function alphabetize_by_last_name( $bp_user_query ) {
    if ( 'alphabetical' == $bp_user_query->query_vars['type'] )
        $bp_user_query->uid_clauses['orderby'] = "ORDER BY substring_index(u.value, ' ', -1)";
}
add_action ( 'bp_pre_user_query', 'alphabetize_by_last_name' );

// To reflect the alphabetical sorting of the member directory, you
// could also format the names to show the last name first. Here is
// a helper function to format names as follows: Last, First Middle
// Etc.
//
// To use this function every time a user's name is shown or queried,
// simply add it as a filter:
//
// `add_filter ('bp_get_member_name', 'format_last_name_first' );`
//
// To only reformat the name in the member directory, change your
// members/members-loop.php file in your (child)theme. Look for
// `bp_member_name()`
// and replace it with
// `echo format_last_name_first ( bp_get_member_name() );`

/**
 * Helper function for formatting a name: Last, First Middle Etc.
 *
 * @param string $name
 * @return string Formatted name
 */
function format_last_name_first( $name ) {
    if ( $first_space = strrpos ( $name, " ") )
        $name = substr( $name, $first_space + 1 ) . ", " . substr ( $name, 0, $first_space );
    return $name;
}

// BONUS: To make alphabetical sorting the default sorting, use the
// function below. 
//
// In order for this to work properly, `<option value="alphabetical">`
// must be the first option for the members-order-select in
// members/index.php.

function sort_members_alphabetically( $qs = '', $object = false ) {
    if( $object != 'members' ) //for members only
        return $qs;

    if ( empty ( $qs ) || ! strpos ( $qs, "type=" ) )
        $qs .= "type=alphabetical&action=alphabetical&page=1";

    return $qs;
}
add_action( 'bp_ajax_querystring', 'sort_members_alphabetically', 11, 2 );

very cool