Add form field to custom column in the Table of Rates

betrs-add-column-data.php

/**
 * Add form field to custom column in the Table of Rates
 *
 * @return string
 */
function betrs_add_column_data( $content, $item ) {
    // find previously saved value
    $saved = ( isset( $item['provider'] ) ) ? sanitize_text_field( $item['provider'] ) : '';

    // array of shipping providers
    $providers = array( 
        'US Postal Service',
        'FedEx',
        'UPS'
    );

    // setup form field
    $content = '<select name="provider[' . $item['option_ID'] . '][' . $item['row_ID'] . ']">';

    foreach( $providers as $name ) {
        $content .= '<option ' . selected( $name, $saved, false ) . '>' . $name . '</option>';
    }

    $content .= '</select>';

    return $content;
}
add_filter( 'betrs_shipping_table_column_provider', 'betrs_add_column_data', 10, 2 );