Hi,

The category x axis assumes that you are specifying categories. It assumes that all categories are represented in the data assigned to each series and are in the same order. If it didn't make this assumption then it would perform work to align and reorder the data, which would hurt the performance in the case that the data was already suitably aligned (not efficient to detect), which is assumed to be the most common case. It's almost always more efficient to ask the data tier to align the data rather than doing it in the UI tier.

Nevertheless, with Date categories, you can often wind up in a situation where you have different number of values, that are not aligned with each other, etc. One option is to align the data that is in the different series, and add 0 or null for the categories that aren't represented in one of the data sets. Most of the series types will support either not displaying a null value or optionally doing a linear interpolation to present a projected missing value.

We have been evaluating whether we can provide an adapter or build something into the chart than can, optionally, provide this function to the user.

Another option for date data, is that we will release a category date axis with the RTM version of the chart that displays values exactly scaled to their date value, rather than treating the dates as string categories, evenly spaced. This axis type is tolerant of non-aligned data.

In the meantime, this sample shows how you could use an adapter to align data for the series of a chart before binding:

var data1, data2, combinedData;

            data1 = [{ label: "aug-2010", value: 2 },
            { label: "sep-2010", value: 4 },
            { label: "nov-2010", value: 5 },
            { label: "dec-2010", value: 3 },
            { label: "jan-2011", value: 2}];

            data2 = [{ label: "sep-2010", value: 3 },
            { label: "oct-2010", value: 6 },
            { label: "nov-2010", value: 4 },
            { label: "jan-2011", value: 3}];

            var combineData = function (comparison, getCategory, getValue) {
                var args = Array.prototype.slice.call(arguments),
                allCategories = [],
                categoryHash = {},
                uniqueCategories = [], combined = [],
                indices = [], i = 0, j = 0, done = false,
                category = "", newCat,
                index = 0;

                args.shift();
                args.shift();
                args.shift();

                for (i = 0; i < args.length; i++) {
                    indices.push(0);
                    for (j = 0; j < args[i].length; j++) {
                        allCategories.push({ category: getCategory(args[i][j]), index: i, item: args[i][j] });
                    }
                }
                allCategories.sort(function (c1, c2) {
                    return comparison(c1.category, c2.category);
                });

                for (i = 0; i < allCategories.length; i++) {
                    category = allCategories[i].category;
                    index = allCategories[i].index;

                    if (typeof categoryHash[category] == "undefined") {
                        newCat = { category: category }
                        categoryHash[category] = newCat;
                        for (j = 0; j < args.length; j++) {
                            newCat["value" + index] = null;
                        }
                        newCat["value" + index] = getValue(allCategories[i].item);
                        uniqueCategories.push(newCat);
                    } else {
                        categoryHash[category]["value" + index] = getValue(allCategories[i].item);
                    }
                }

                return uniqueCategories;
            }

            var months = months = {
                'jan': 1, 'feb': 2, 'mar': 3,
                'apr': 4, 'may': 5, 'jun': 6,
                'jul': 7, 'aug': 8, 'sep': 9,
                'oct': 10, 'nov': 11, 'dec': 12
            };

            var catParse = function (cat) {
                var vals = cat.split('-'),
                month = months[vals[0]],
                year = parseInt(vals[1]);

                return new Date(year, month, 1);
            };

            combinedData = combineData(function (d1, d2) {
                var date1 = catParse(d1), date2 = catParse(d2);
                if (date1 < date2) {
                    return -1;
                }
                if (date2 > date1) {
                    return 1;
                }
                return 0;
            },
            function (item) { return item.label },
            function (item) { return item.value },
            data1, data2);

            $("#container").igDataChart({
                width: "500px",
                height: "500px",
                dataSource: combinedData,
                axes: [{
                    name: "xAxis",
                    type: "categoryX",
                    label: "category"
                },
                {
                    name: "yAxis",
                    type: "numericY",
                    minimumValue: 0
                }],
                series: [{
                    name: "series1",
                    title: "Test Series",
                    type: "column",
                    xAxis: "xAxis",
                    yAxis: "yAxis",
                    valueMemberPath: "value0"
                },
                {
                    name: "series2",
                    title: "Test Series",
                    type: "column",
                    xAxis: "xAxis",
                    yAxis: "yAxis",
                    valueMemberPath: "value1"
                }],
                horizontalZoomable: true,
                verticalZoomable: true,
                windowResponse: "immediate"
            });

Which produces this output: