Hi there... i am still using old version Infragistics ASP.Net 2015.1 via MVC on VS 2015...
sample:

settings.ColumnSetting().ColumnKey("CID").Required(false).ReadOnly(false)
                            .EditorType(ColumnEditorType.Combo)
                            .ComboEditorOptions(co => co.DataSource(companies).ID("CIDCombo").ValueKey("CO").TextKey("CO").Mode(ComboMode.DropDown).EnableClearButton(false)
                            .MultiSelectionSettings(ms => ms.Enabled(true).ShowCheckBoxes(true).ItemSeparator(","))
                            .DropDownOrientation(ComboDropDownOrientation.Bottom)
                        )

so, my db-table field CID (comma delimited string values) would require to bind to this combo editor with multi selection capability...  however, i cannot get the API required per your javascript sample...  please, advise if it's because either the version I have is too old or because I might be missing any references...  if you have a sample for my situation i will appreciate it...

Note: I want to stick to the MVC way if possible...

@using Infragistics.Web.Mvc




    <script type="text/javascript">
        var northwindProductsJSON = [
      { "ID": 0, "Name": "Bread", "Description": "Whole grain bread", "Price": "2.5", "CategoryID": "Food" },
      { "ID": 1, "Name": "Milk", "Description": "Low fat milk", "Price": "3.5", "CategoryID": "Beverages" },
      { "ID": 2, "Name": "Vint Soda", "Description": "Americana Variety ", "Price": "20.9", "CategoryID": "Beverages" },
      { "ID": 3, "Name": "Havina Cola", "Description": "The Original Key Lime Cola", "Price": "19.9", "CategoryID": "Beverages" },
      { "ID": 4, "Name": "Fruit Punch", "Description": "Mango flavor, 8.3 Ounce Cans (Pack of 24)", "Price": "22.99", "CategoryID": "Beverages" },
      { "ID": 5, "Name": "Cranberry Juice", "Description": "16-Ounce Plastic Bottles (Pack of 12)", "Price": "22.8", "CategoryID": "Beverages" },
      { "ID": 6, "Name": "Pink Lemonade", "Description": "36 Ounce Cans (Pack of 3)", "Price": "18.8", "CategoryID": "Beverages" },
      { "ID": 7, "Name": "DVD Player", "Description": "1080P Upconversion DVD Player", "Price": "35.88", "CategoryID": "Electronics" },
      { "ID": 8, "Name": "LCD HDTV", "Description": "42 inch 1080p", "Price": "1088.8", "CategoryID": "Electronics" }
        ],
         northWindCategoriesJSON = [
             { "ID": 0, "Name": "Food" },
             { "ID": 1, "Name": "Beverages" },
             { "ID": 2, "Name": "Electronics" }
         ];
        $(function () {

            $("#grid").igGrid({
                dataSource: northwindProductsJSON,
                autoGenerateColumns: true,
                primaryKey: "ID",
                autoCommit: true,
            features: [
            {
              name: 'Updating',
               
                columnSettings: [{
                    //The combo is defined as a custom editor provider. Combo options are defined under 'editorOptions'.
                    columnKey: "CategoryID",
                   editorProvider: new $.ig.ComboEditorProviderCustom(),
                    editorOptions: {
                        mode: "dropdown",
                        dataSource: northWindCategoriesJSON,
                        textKey: "Name",
                        valueKey: "Name",
                        allowCustomValue: true,
                        multiSelection: {
                            enabled: true,
                            showCheckboxes: true,
                            itemSeparator: ', '
                        }
                    }
                }]
            }]
        });
        });
        $(function () {
        $.ig.ComboEditorProviderCustom = $.ig.EditorProviderCombo.extend({
            getValue: function () {
                var val = this.editor.value();
                var text = this.editor.text();
                if ($.type(val) === "array" && val.length) {
                    //When the passed value is of complex type return the text instead. 
                    //This will be the value saved in the grid data source after editing ends.
                    return text;
                }
                return val;
            },
            setValue: function (val, fire) {
                var array = [];
                this.editor.deselectAll();
                if (this.options.multiSelection.enabled && val.contains(this.options.multiSelection.itemSeparator)) {
                    //if multiSelection is enabled and the value passed from the grid cell to the edito contains the specified itemSeparator
                    //Then split the value by the separator and set a complex value back to the editor so that the matching items will get selected.
                    array = val.split(this.options.multiSelection.itemSeparator);
                    return this.editor.value(array, null, fire);
                }
                this.editor.value(val, null, fire);
            }
        });
        });
    </script>


    
<body>
    <table id="grid"></table>
</body>

Am getting error in this line 

editorProvider: new $.ig.ComboEditorProviderCustom(),

Error is Object doesn't support this action

George,

Please share a sample containing your attempt a creating the editor provider that reproduces the error 'Unable to create editorprovider' so that we can review what is happening.