_chart._doColumnValueFormat = function (v, d) {
        return ((typeof v === 'function') ?
                v(d) :                          // v as function
                ((typeof v === 'string') ?
                 d[v] :                         // v is field name string
                 v.format(d)                        // v is Object, use fn (element 2)
                )
               );
    };