Footer Callback for Multiple Columns

Dear Sirs

Refer to this link: https://datatables.net/examples/advanced_init/footer_callback.html

How can we have pageTotal for multiple columns, for example if there are numerical data at (4th, 5th, 6th columns) all need a pageTotal. how will the below script be amended ?

"footerCallback": function ( row, data, start, end, display ) {
var api = this.api(), data;

        // Remove the formatting to get integer data for summation
        var intVal = function ( i ) {
            return typeof i === 'string' ?
                i.replace(/[\$,]/g, '')*1 :
                typeof i === 'number' ?
                    i : 0;
        };

        // Total over all pages
        total = api
            .column( 4 )
            .data()
            .reduce( function (a, b) {
                return intVal(a) + intVal(b);
            }, 0 );

        // Total over this page
        pageTotal = api
            .column( 4, { page: 'current'} )
            .data()
            .reduce( function (a, b) {
                return intVal(a) + intVal(b);
            }, 0 );

        // Update footer
        jQuery( api.column( 4 ).footer() ).html(
           // '$'+pageTotal +' ( $'+ total +' total)'
           pageTotal.toFixed( 2 )
        );
    },