Data Aggregation

• Aug 21, 2019
• 6 minutes to read

The Chart Control can use an aggregate function to group raw data source values and show aggregates as series points. You can use aggregation to show grouped data and decrease the number of visible points in a chart. Data aggregation is only available for argument axes (x-axes).

• Aggregation vs Summaries
• Aggregation Basics
• Aggregate Date-Time Data
• Aggregate Numeric Data
• Aggregate Qualitative Data
• Aggregate an Individual Series’s Data
• Create a Custom Aggregate Function

Aggregation vs Summaries

In addition to Aggregation, the Chart Control provides Summaries that also allow you to group raw data values.

	Aggregation	Summary
Store Data	Chart stores raw data source values.	Chart stores summarized values.
Change Detail Level	Chart re-calculates data in memory.	Chart re-loads data from the data source.
Behave on Zoom	If the automatic scale options are used, Chart recalculates value aggregates when it is zoomed.	Chart does not re-calculate aggregated values when it is zoomed.
Memory Consumption	High	Low

Aggregation Basics

When the aggregation is enabled, the chart splits the x-axis into intervals (the x-axis measurement unit value defines the intervals), and uses an aggregate function to aggregate data for each interval.

The AggregateFunction enumeration lists the available aggregate functions:

• Average (a default function)
• Count
• Financial (Use it for financial series.)
• Histogram (See the Histogram topic for more information.)
• Maximum
• Minimum
• Sum
• Custom (Refer to the Create an Aggregate Function section for more information.)

Scale options assigned to the x-axis’s ~ScaleOptions property store aggregation-related settings. You can use the following option types:

Options	Description	How to use
Automatic Date-Time and Automatic Numeric	The chart control defines the optimal measurement unit for an axis based on the data set’s values, the Chart Control’s current size, and zoom level.	For date-time axes. Assign a AutomaticDateTimeScaleOptions object to the AxisX2D.DateTimeScaleOptions, AxisX3D.DateTimeScaleOptions or RadarAxisX2D.DateTimeScaleOptions property. For numeric axes. Assign a AutomaticNumericScaleOptions object to the AxisX2D.NumericScaleOptions, AxisX3D.NumericScaleOptions or CircularAxisX2D.NumericScaleOptions property.
Manual Date-Time and Manual Numeric	You can specify the axis measurement unit.	For date-time axes. Assign a ManualDateTimeScaleOptions (or its descendant) object to the AxisX2D.DateTimeScaleOptions, AxisX3D.DateTimeScaleOptions or RadarAxisX2D.DateTimeScaleOptions property. For numeric axes. Assign a ManualNumericScaleOptions (or its descendant) object to the AxisX2D.NumericScaleOptions, AxisX3D.NumericScaleOptions or CircularAxisX2D.NumericScaleOptions property.
Qualitative	Chart aggregates point values if points have equal arguments.	For qualitative axes. Assign QualitativeScaleOptions to the AxisX2D.QualitativeScaleOptions or AxisX3D.QualitativeScaleOptions property.

Note

Axes that have the Continuous scale type (ContinuousDateTimeScaleOptions and ContinuousNumericScaleOptions) do not support aggregation.

Aggregate Date-Time Data

The following images show aggregated date-time data:

MeasureUnit = Year; GridAlignment = Year

MeasureUnit = Month; GridAlignment = Year

MeasureUnit = Month; GridAlignment = Month

The examples below use an Average function to aggregate date-time data:

Automatic Mode

XAML

<dxc:XYDiagram2D>
    <dxc:XYDiagram2D.AxisX>
        <dxc:AxisX2D>
            <dxc:AxisX2D.DateTimeScaleOptions>
                <dxc:AutomaticDateTimeScaleOptions AggregateFunction="Average"/>
            </dxc:AxisX2D.DateTimeScaleOptions>                    
        </dxc:AxisX2D>
    </dxc:XYDiagram2D.AxisX>
    <!--...-->
</dxc:XYDiagram2D>

Manual Mode

XAML

<dxc:XYDiagram2D>
    <dxc:XYDiagram2D.AxisX>
        <dxc:AxisX2D>
            <dxc:AxisX2D.DateTimeScaleOptions>
                <dxc:ManualDateTimeScaleOptions AggregateFunction="Average" 
                                                MeasureUnit="Year" 
                                                GridAlignment="Year"/>      
            </dxc:AxisX2D.DateTimeScaleOptions>        
        </dxc:AxisX2D>
    </dxc:XYDiagram2D.AxisX>
    <!--...-->
</dxc:XYDiagram2D>

The examples above use the following API members:

Member	Description
AxisX2D.DateTimeScaleOptions	Provides access to the options that define the behavior of a date-time X-scale when its mode is manual, automatic or continuous.
AutomaticDateTimeScaleOptions	Contains settings for a date-time axis data when its scale mode is automatic.
ManualDateTimeScaleOptions	Contains settings for a date-time axis data when its scale mode is manual.

Form a Custom Measurement Unit

You can use the ManualDateTimeScaleOptions.MeasureUnitMultiplier property with ManualDateTimeScaleOptions.MeasureUnit to specify a new measurement unit.

MeasureUnit = Month; MeasureUnitMultiplier = 1

MeasureUnit = Month; MeasureUnitMultiplier = 6

XAML

<dxc:XYDiagram2D>
    <dxc:XYDiagram2D.AxisX>
        <dxc:AxisX2D>
            <dxc:AxisX2D.DateTimeScaleOptions>
                <dxc:ManualDateTimeScaleOptions AggregateFunction="Average" 
                                                GridAlignment="Year" 
                                                MeasureUnit="Month" 
                                                MeasureUnitMultiplier="6"/>
            </dxc:AxisX2D.DateTimeScaleOptions>                    
        </dxc:AxisX2D>
    </dxc:XYDiagram2D.AxisX>
</dxc:XYDiagram2D>

See also the following examples:

• How to: Use Manual Date-Time Scale Options of an Axis
• How to: Use a Custom Measure Units in Automatic Date-Time Scale Mode

Aggregate Numeric Data

The following images show aggregated numeric data:

AggregationFunction = Average; MeasureUnit = 10000

AggregationFunction = Average; MeasureUnit = 1000

The examples below use an Average function to aggregate numeric data:

Automatic Mode

XAML

<dxc:XYDiagram2D>
    <dxc:XYDiagram2D.AxisX>
        <dxc:AxisX2D>
            <dxc:AxisX2D.NumericScaleOptions>
                <dxc:AutomaticNumericScaleOptions AggregateFunction="Average"/>
            </dxc:AxisX2D.NumericScaleOptions>
        </dxc:AxisX2D>
    </dxc:XYDiagram2D.AxisX>
</dxc:XYDiagram2D>

Manual Mode

XAML

<dxc:XYDiagram2D>
    <dxc:XYDiagram2D.AxisX>
        <dxc:AxisX2D>
            <dxc:AxisX2D.NumericScaleOptions>
                <dxc:ManualNumericScaleOptions AggregateFunction="Average" 
                                               MeasureUnit="1000"/>       
            </dxc:AxisX2D.NumericScaleOptions>
        </dxc:AxisX2D>
    </dxc:XYDiagram2D.AxisX>
</dxc:XYDiagram2D>

The examples above use the following API members:

Member	Description
AxisX2D.NumericScaleOptions	Provides access to the options that define the behavior of a numeric X-scale when its mode is manual, automatic or continuous.
AutomaticNumericScaleOptions	Contains settings for a numeric axis data when its scale mode is automatic.
ManualNumericScaleOptions	Contains settings for a numeric axis data when its scale mode is manual.

See also the following examples:

• How to: Use Manual Numeric Scale Options of an Axis
• How to: Use a Custom Measure Unit in Automatic Numeric Scale Mode

Aggregate Qualitative Data

The following images show non-aggregated and aggregated qualitative data:

AggregationFunction = None

AggregationFunction = Average

AggregationFunction = Sum

The example below uses a Sum function to aggregate qualitative data:

XAML

<dxc:XYDiagram2D>
    <dxc:XYDiagram2D.AxisX>
        <dxc:AxisX2D>
            <dxc:AxisX2D.QualitativeScaleOptions>
                <dxc:QualitativeScaleOptions AggregateFunction="Sum"/>
            </dxc:AxisX2D.QualitativeScaleOptions>
        </dxc:AxisX2D>
    </dxc:XYDiagram2D.AxisX>   
</dxc:XYDiagram2D>

Aggregate an Individual Series’s Data

You can apply different aggregate functions to series that are bound to the same x-axis. In this case, the aggregate function applied to a series has higher priority than the axis’s aggregate function. To specify a series’s aggregate function, use the XYSeries.AggregateFunction property.

The following example uses the Financial function to aggregate the Stock series and the Sum function - the Bar series:

XAML

<dxc:XYDiagram2D>
    <dxc:StockSeries2D
        x:Name="stockSeries"
        DisplayName="Price"
        ArgumentDataMember="DateTimeStamp"
        OpenValueDataMember="Open"
        HighValueDataMember="High"
        LowValueDataMember="Low"
        CloseValueDataMember="Close"
        AggregateFunction="Financial">
    </dxc:StockSeries2D>
    <dxc:BarSideBySideSeries2D
        x:Name="volumeSeries"
        DisplayName="Volume"
        ArgumentDataMember="DateTimeStamp"
        ValueDataMember="Volume"
        AggregateFunction="Sum">
    </dxc:BarSideBySideSeries2D>
</dxc:XYDiagram2D>

Create a Custom Aggregate Function

• Set the AggregateFunction (AutomaticDateTimeScaleOptions.AggregateFunction, ManualDateTimeScaleOptions.AggregateFunction, AutomaticNumericScaleOptions.AggregateFunction, ManualNumericScaleOptions.AggregateFunction, QualitativeScaleOptions.AggregateFunction or XYSeries.AggregateFunction) property to Custom.

• Develop a class that inherits the CustomAggregateFunction class.

• Override the CustomAggregateFunction.Calculate(GroupInfo) method.

• Initialize the CustomAggregateFunction (AutomaticDateTimeScaleOptions.CustomAggregateFunction, ManualDateTimeScaleOptions.CustomAggregateFunction, AutomaticNumericScaleOptions.CustomAggregateFunction, ManualNumericScaleOptions.CustomAggregateFunction, QualitativeScaleOptions.CustomAggregateFunction or XYSeries.CustomAggregateFunction) property with a newly created aggregate function class instance.

The example below shows how to implement an aggregate function:

XAML

<dxc:XYDiagram2D>
    <dxc:XYDiagram2D.AxisX>
        <dxc:AxisX2D>
            <dxc:AxisX2D.DateTimeScaleOptions>
                <dxc:AutomaticDateTimeScaleOptions AggregateFunction="Custom">
                    <dxc:AutomaticDateTimeScaleOptions.CustomAggregateFunction>
                        <local:StandardDeviationAggregateFunction/>
                    </dxc:AutomaticDateTimeScaleOptions.CustomAggregateFunction>
                </dxc:AutomaticDateTimeScaleOptions>
            </dxc:AxisX2D.DateTimeScaleOptions>
            <!--...-->                      
        </dxc:AxisX2D>
    </dxc:XYDiagram2D.AxisX>
    <!--...-->
</dxc:XYDiagram2D>

C#

using DevExpress.Xpf.Charts;
using System;
using System.Collections.Generic;
using System.Globalization;
using System.IO;
using System.Linq;
using System.Windows;
using System.Xml.Linq;

namespace DateTimeAggregation {
    class StandardDeviationAggregateFunction : CustomAggregateFunction {
        public override string ToString() {
            return "StdDev (Custom)";
        }
        public override double[] Calculate(GroupInfo groupInfo) {
            double sum = 0.0;
            foreach(double value in groupInfo.Values1) {
                sum += value;
            }
            int len = groupInfo.Values1.Count();
            double averageAmount = sum / len;
            double standardDeviationSquareSum = 0.0;
            foreach(double value in groupInfo.Values1) {
                double deviation = value - averageAmount;
                standardDeviationSquareSum += deviation * deviation;
            }
            double stdDev = Math.Sqrt(standardDeviationSquareSum / len);
            return new double[1] { stdDev };
        }
    }
}

VB.NET

Imports DevExpress.Xpf.Charts
Imports System
Imports System.Collections.Generic
Imports System.Globalization
Imports System.IO
Imports System.Linq
Imports System.Windows
Imports System.Xml.Linq

Namespace DateTimeAggregation
    Class StandardDeviationAggregateFunction
        Inherits CustomAggregateFunction

        Public Overrides Function ToString() As String
            Return "StdDev (Custom)"
        End Function

        Public Overrides Function Calculate(ByVal groupInfo As GroupInfo) As Double()
            Dim sum As Double = 0.0

            For Each value As Double In groupInfo.Values1
                sum += value
            Next

            Dim len As Integer = groupInfo.Values1.Count()
            Dim averageAmount As Double = sum / len
            Dim standardDeviationSquareSum As Double = 0.0

            For Each value As Double In groupInfo.Values1
                Dim deviation As Double = value - averageAmount
                standardDeviationSquareSum += deviation * deviation
            Next

            Dim stdDev As Double = Math.Sqrt(standardDeviationSquareSum / len)
            Return New Double(0) {stdDev}
        End Function
    End Class
End Namespace