Select inputs on a individual column with joined data

I'm using the code from the example "Individual column searching (select inputs)" on a column showing joined data. But the drop down list shows only [object Object], [object Object], [object Object] when 3 different data is joined. I want it to sort out those lines where data1 is represented no matter if it's joined with data2 or data3 or alone. Is that possible?
Best regards Claus

initComplete: function () {
            this.api().columns(4).every( function () {
                var column = this;
                var select = $('<select><option value=""></option></select>')
                    .appendTo( $(column.header()).empty() )
                    .on( 'change', function () {
                        var val = $.fn.dataTable.util.escapeRegex(
                            $(this).val()
                        );
 
                        column
                            .search( val ? '^'+val+'$' : '', true, false )
                            .draw();
                    } );
 
                column.data().unique().sort().each( function ( d, j ) {
                    select.append( '<option value="'+d+'">'+d+'</option>' )
                } );
            } );
        },