Making my custom column sortable

Question

I am using custom post type with a relationship field with ACF and trying to get a column of number of times the "location" has been used in posts (this is my custom post type - location).

I have everything working beside the sortable option which I can't seem to figure out.

Any help will be appreciated, Here's my code so far:

function change_columns( $cols ) {
  $cols = array(
    'cb'       => '<input type="checkbox" />',
    'title'      => __( 'Title',      'trans' ),
    'number'      => __( 'Number',      'trans' ),
    'author'      => __( 'Author',      'trans' ),
    'Date'      => __( 'Date',      'trans' ),  
  );
  return $cols;
}
add_filter( "manage_edit-usa-locations_columns", "change_columns" );

function columns_content_only_locations($column_name, $post_ID) {
    if ($column_name == 'number') {

    $locations = get_posts(array(
        'post_type' => 'post',
        'category'  => '3',
        'numberposts'=>-1,
        'orderby' => 'title',
        'posts_per_page'   => -1,
        'meta_query' => array(
            array(
                'key' => 'headquarters', // name of custom field
                'value' => '"' . get_the_ID() . '"', // matches exaclty "123", not just 123. This prevents a match for "1234"
                'compare' => 'LIKE'
            )
        )
    ));

    $totalCount = count( $locations );
    echo $totalCount;

    }
}

add_action('manage_usa-locations_posts_custom_column', 'columns_content_only_locations', 10, 2);

// Make these columns sortable
function sortable_columns() {
  return array(
    'number'      => 'number',
    'title'      => 'title',
  );
}

add_filter( "manage_edit-usa-locations_sortable_columns", "sortable_columns" );


function number_column_order( $vars ) {
    if ( isset( $vars['orderby'] ) && 'count' == $vars['orderby'] ) {
        $vars = array_merge( $vars, array(
            'meta_key' => 'count',
            'orderby' => 'meta_value_num'
        ) );
    }

    return $vars;
}
add_filter( 'request', 'number_column_order' );

Answer 1

in the action request, the keys meta_key and orderby already exists then try to overwrite like this :

if ( isset( $vars['orderby'] ) && 'count' == $vars['orderby'] ) {

    $vars["meta_key"] = "count";
    $vars["orderby"] = "meta_value_num";

}