My buddy, who is learning Silverlight and MVVM, has been using the new Chart controls from the Silverlight Toolkit.  The road block he was having was being able to data bind a collection of collections to a Chart's series.  This was difficult because the Series property of the Chart does not play nice.  So me being such a wonderful friend, I whipped up a quick attached behavior to allow this.

Here is the usage:

<Charting:Chart x:Name="chart"
Helper:ChartHelper.DependentValueBinding="Value"
Helper:ChartHelper.IndependentValueBinding="Key"
Helper:ChartHelper.Title="TitlePropertyOnCollection"
Helper:ChartHelper.SeriesType="Line"
Helper:ChartHelper.SeriesSource="{Binding Path=MyCollectionofCollections}" />

Here is the code:

public enum SeriesType
{
    Line,
    Bar,
    Column,
    Scatter,
    Pie
}

public class ChartHelper
{
    #region SeriesSource

    public static readonly DependencyProperty SeriesSourceProperty =
            DependencyProperty.RegisterAttached("SeriesSource", 
                                                typeof(IEnumerable), 
                                                typeof(ChartHelper),
                                                new PropertyMetadata(SeriesSourceChanged));

    public static IEnumerable GetSeriesSource(DependencyObject d)
    {
        return (IEnumerable)d.GetValue(SeriesSourceProperty);
    }

    public static void SetSeriesSource(DependencyObject d, IEnumerable value)
    {
        d.SetValue(SeriesSourceProperty, value);
    }

    #endregion

    #region DependentValueBinding

    public static readonly DependencyProperty DependentValueBindingProperty =
        DependencyProperty.RegisterAttached("DependentValueBinding", 
                                            typeof(string), 
                                            typeof(ChartHelper),
                                            null);

    public static string GetDependentValueBinding(DependencyObject d)
    {
        return (string)d.GetValue(DependentValueBindingProperty);
    }

    public static void SetDependentValueBinding(DependencyObject d, string value)
    {
        d.SetValue(DependentValueBindingProperty, value);
    }

    #endregion

    #region IndependentValueBinding

    public static readonly DependencyProperty IndependentValueBindingProperty =
        DependencyProperty.RegisterAttached("IndependentValueBinding", 
                                            typeof(string), 
                                            typeof(ChartHelper),
                                            null);

    public static string GetIndependentValueBinding(DependencyObject d)
    {
        return (string)d.GetValue(IndependentValueBindingProperty);
    }

    public static void SetIndependentValueBinding(DependencyObject d, string value)
    {
        d.SetValue(IndependentValueBindingProperty, value);
    }

    #endregion

    #region Title

    public static readonly DependencyProperty TitleProperty =
        DependencyProperty.RegisterAttached("Title", 
                                            typeof(string), 
                                            typeof(ChartHelper),
                                            null);

    public static string GetTitle(DependencyObject d)
    {
        return (string)d.GetValue(TitleProperty);
    }

    public static void SetTitle(DependencyObject d, string value)
    {
        d.SetValue(TitleProperty, value);
    }

    #endregion

    #region SeriesType

    public static readonly DependencyProperty SeriesTypeProperty =
        DependencyProperty.RegisterAttached("SeriesType", 
                                            typeof(SeriesType), 
                                            typeof(ChartHelper),
                                            new PropertyMetadata(SeriesType.Bar));

    public static SeriesType GetSeriesType(DependencyObject d)
    {
        return (SeriesType)d.GetValue(SeriesTypeProperty);
    }

    public static void SetSeriesType(DependencyObject d, SeriesType value)
    {
        d.SetValue(SeriesTypeProperty, value);
    }

    #endregion

    #region SeriesStyle

    public static readonly DependencyProperty SeriesStyleProperty =
        DependencyProperty.RegisterAttached("SeriesStyle", 
                                            typeof(Style), 
                                            typeof(ChartHelper),
                                            null);

    public static Style GetSeriesStyle(DependencyObject d)
    {
        return (Style)d.GetValue(SeriesStyleProperty);
    }

    public static void SetSeriesStyle(DependencyObject d, Style value)
    {
        d.SetValue(SeriesStyleProperty, value);
    }

    #endregion

    private static void SeriesSourceChanged(DependencyObject d, 
                                            DependencyPropertyChangedEventArgs e)
    {
        if(!(d is Chart))
        {
            throw new Exception("Series attached property only works on a Chart type");
        }

        var chart = d as Chart;

        /* Clear out any old series in the chart */
        chart.Series.Clear();

        /* Get our collection of data we need for each series */
        var chartSeriesSource = e.NewValue as IEnumerable;

        if(chartSeriesSource == null)
            throw new Exception("The SeriesSource does not support IEnumerable");

        /* Loop over each collection of data */
        foreach(var dataSource in chartSeriesSource)
        {
            DynamicSeries series;

            /* Find out what type of series we want to use */
            var seriesType = GetSeriesType(chart);

            switch(seriesType)
            {
                case SeriesType.Line:
                    series = new LineSeries();
                    break;
                case SeriesType.Bar:
                    series = new BarSeries();
                    break;
                case SeriesType.Column:
                    series = new ColumnSeries();
                    break;
                case SeriesType.Pie:
                    series = new PieSeries();
                    break;
                case SeriesType.Scatter:
                    series = new ScatterSeries();
                    break;
                default:
                    throw new ArgumentOutOfRangeException();
            }

            /* Get and set the style of the newly created series */
            var seriesStyle = GetSeriesStyle(chart);
            series.Style = seriesStyle;
            
            string titleBindingName = GetTitle(chart);
            
            if (!string.IsNullOrEmpty(titleBindingName))
            {
                /* Do some binding of the Title property */
                var titleBinding = new Binding(titleBindingName)
                {
                    Source = series.Title, Mode = BindingMode.TwoWay
                };

                series.SetBinding(Series.TitleProperty, titleBinding);
            }

            /* Setup the bindings configured in the attached properties */
            series.DependentValueBinding = new Binding(GetDependentValueBinding(chart));
            series.IndependentValueBinding = new Binding(GetIndependentValueBinding(chart));

            /*Set the ItemsSource property, which gives the data to the series to be rendered */
            series.ItemsSource = dataSource as IEnumerable;

            /* Add the series to the chart */
            chart.Series.Add(series);
        }
    }
}