How to summarize multiple columns

smason

I have the code on this page working:
https://datatables.net/examples/advanced_init/footer_callback.html

However I don't understand how to summarize multiple columns, the example just summarizes one. I have a table where I want to summarize 3 columns and average a final column. How is that accomplished?

tangerine

The function you have copied refers to "column( 4 )" throughout. You could rewrite it to accept a variable column number as a passed parameter.

smason

Yes, I understand that it uses column(4) throughout. My javascript skills are not good enough to know how to make that a dynamic variable which is why I needed help with that snippet.

But anyhow I solved this issue a different way:
First use the SUM Plugin Declare it before the datatable initialization but inside document ready block:

// SUM PLUGIN
    jQuery.fn.dataTable.Api.register( 'sum()', function ( ) {
        return this.flatten().reduce( function ( a, b ) {
            if ( typeof a === 'string' ) {
                a = a.replace(/[^\d.-]/g, '') * 1;
            }
            if ( typeof b === 'string' ) {
                b = b.replace(/[^\d.-]/g, '') * 1;
            }

            return a + b;
        }, 0 );
    } );

Now the footer callback inside the datatable definition looks like this:

"footerCallback": function () {
    var api = this.api(),
    columns = [2, 3, 4]; // Add columns here

    for (var i = 0; i < columns.length; i++) {
    //summarize only the visible columns
        $('tfoot th').eq(columns[i]).html('' + api.column(columns[i], { filter: 'applied', page: 'current' }).data().sum());
    }
} //end footerCallback

allan

That's perfect and exactly what tangerine was suggesting.

Nice one

Allan