Select User Role on Registration

I tried WP Roles at Registration (out of date but tried anyway), ProfilePress (tested and working on my version of WorPress) and one more I can’t recall (also out of date but tried anyway).

I understand GeoDir can work with BuddyPress and think BuddyPress has this function? However I don’t want all the social side of BuddyPress on my site. Is it possible to just change the registration form but leave the rest of the site untouched?

Assuming GD just pulls out the WordPress registration and puts it onto a different page, I should in theory be able to just use a registration form-modifying plugin, and the changes that make will appear in the form that GD displays, right?

As the plugins (one confirmed working on my version of WP) didn’t work, I wondered if maybe the GD registration wasn’t just the standard WP registration form.

All three plugins I used claim to put user role selection on the signup page, that is what I want. I can’t find the feature in BuddyPress, I can find the option to add additional fields but not the option to make one of those fields user role selection.

Searching online I’ve found this code:

<?php
//1. Add a new form element...
add_action( 'register_form', 'myplugin_register_form' );
function myplugin_register_form() {

    global $wp_roles;

    echo '<select name="role" class="input">';
    foreach ( $wp_roles->roles as $key=>$value ):
       echo '<option value="'.$key.'">'.$value['name'].'</option>';
    endforeach;
    echo '</select>';
}

//2. Add validation.
add_filter( 'registration_errors', 'myplugin_registration_errors', 10, 3 );
function myplugin_registration_errors( $errors, $sanitized_user_login, $user_email ) {

    if ( empty( $_POST['role'] ) || ! empty( $_POST['role'] ) && trim( $_POST['role'] ) == '' ) {
         $errors->add( 'role_error', __( '<strong>ERROR</strong>: You must include a role.', 'mydomain' ) );
    }

    return $errors;
}

//3. Finally, save our extra registration user meta.
add_action( 'user_register', 'myplugin_user_register' );
function myplugin_user_register( $user_id ) {

   $user_id = wp_update_user( array( 'ID' => $user_id, 'role' => $_POST['role'] ) );
} ?>

But placing it in functions.php didn’t do anything and I’m not sure where else to put it.