Custom SQL query for PMPro Directory Widget that also filters field values stored as arrays

my-pmpro-directory-widget-sql-parts.php

<?php

function my_pmpro_directory_widget_filter_sql_parts( $sql_parts, $levels, $s, $pn, $limit, $start, $end, $order_by, $order ) {
	global $wpdb;

	// Filter results based on ares of practice is selected.
	if ( ! empty( $_REQUEST['areasofpractice'] ) && is_array( $_REQUEST['areasofpractice'] ) ) {
		$sql_parts['JOIN']    .= " LEFT JOIN $wpdb->usermeta um_areasofpractice ON um_areasofpractice.meta_key = 'areasofpractice' AND u.ID = um_areasofpractice.user_id ";
		$sql_parts['WHERE']   .= ' AND ( ';
		$first_areasofpractice = true;
		foreach ( $_REQUEST['areasofpractice'] as $areasofpractice ) {
			if ( $first_areasofpractice ) {
				$first_areasofpractice = false;
			} else {
				$sql_parts['WHERE'] .= ' OR ';
			}
			$sql_parts['WHERE'] .= " um_areasofpractice.meta_value like '%{$areasofpractice}%' ";
		}
		$sql_parts['WHERE'] .= ' ) ';
	}

	return $sql_parts;
}
add_filter( 'pmpro_member_directory_sql_parts', 'my_pmpro_directory_widget_filter_sql_parts', 10, 9 );

This recipe is included in the blog post on "Allow Users to Filter Results in your Member Directory" at Paid Memberships Pro here: https://www.paidmembershipspro.com/allow-users-to-filter-results-in-your-member-directory/