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 End-User Documentation
View this topic on docs.devexpress.com (Learn more)

Histogram

This topic explains how to customize the Chart Control's axis and series settings to make a histogram.

Required Steps

Optional Steps

Expanded Specify a Data Source

You can provide histogram data to a chart in the following ways:

  • Define a data source field that provides series arguments. You do not have to supply data for series point values. The Chart Control calculates values as aggregates based on the frequency of arguments.

  • You can use a one-dimensional array as a data source. In this case, you do not have to specify the argument data member.

You can use the following API:

Member Description
ChartControl.DataSource (Series.DataSource) Specifies the chart control (series) data source.
Series.ArgumentDataMember Gets or sets the name of the data field which contains arguments for generated series points.

The data structure looks as follows:

Expanded Aggregate Data and Divide an Axis Scale into Bins

The Number of Bins is Auto-Calculated

The Chart control can apply Scott's Normal Reference Rule to compute an optimal number of bins and their ranges:

Specify the Number of Bins

The Chart Control can display a specified number of bins for numeric axes. The bin value range is calculated automatically.

The following code creates a histogram with five bins:

The following table lists the API members used in the code above:

Member Description
CountIntervalNumericScaleOptions (see CountIntervalNumericScaleOptions) These options provide the Count property. Use this property to specify the number of bins).
CountIntervalNumericScaleOptions.Count Gets or sets the number of intervals.

Specify the Bin Size

You can specify the bin size (measured in x-axis units). The number of bins is calculated automatically.

The code below creates bins with a size equal to ten x-axis measurement units:

The following table lists the API members used in the code above:

Member Description
WidthIntervalNumericScaleOptions (see WidthIntervalNumericScaleOptions) The options that provide means to create axis intervals with a specified width.
WidthIntervalNumericScaleOptions.Width Gets or sets the interval width in x-axis measurement units.

Expanded Specify Side Bin Thresholds

You can change thresholds for underflow and overflow bins:

The following code uses the IntervalNumericScaleOptions.UnderflowValue and IntervalNumericScaleOptions.OverflowValue properties to change thresholds. (For date-time axes, use IntervalDateTimeScaleOptions.UnderflowValue and IntervalDateTimeScaleOptions.OverflowValue instead.)

Expanded Specify Bar Width

A histogram can use bars positioned next to each other without gaps to display histogram bins.

Set the BarSeries2DBase.BarWidth property to 1 to remove gaps between bars.

Expanded Configure the Grid and Label Layout

The Chart Control aligns Axis Labels, major grid lines, and major tick marks to the center of each bin. You can also align them to the start of each interval.

Specify the GridLayoutMode (IntervalNumericScaleOptions.GridLayoutMode, DateTimeScaleOptionsBase.GridLayoutMode or QualitativeScaleOptions.GridLayoutMode) property to change the axis label, grid line, or tick mark alignment.

Expanded Customize Axis Label Text

You can format label text for axis scale intervals and the underflow/overflow bins.

The following table lists the API members the code above uses:

Member Description
IntervalNumericScaleOptions.Pattern Gets or sets a format string that configures text for the interval Axis Labels and crosshair labels.
IntervalNumericScaleOptions.UnderflowValuePattern Gets or sets a format string that configures text for the underflow interval Axis Labels and crosshair labels.
IntervalNumericScaleOptions.OverflowValuePattern Gets or sets a format string that configures text for the overflow interval Axis Labels and crosshair labels.

Patterns can contain regular text (displayed as is) and value placeholders in braces. To format numeric and date/time values, you can apply Format Specifiers. Use a colon to separate a placeholder and its format specifier. In XAML, insert an escape sequence ({}) into the beginning of a pattern if it starts with a placeholder.

The following table contains the available placeholders:

Placeholder Description
{OB} Displays an opening bracket.
{CB} Displays a closing bracket.
{OS} Displays the greater than sign.
{US} Displays the less than or less than or equal to sign.
{A1} Displays the interval start value.
{A2} Displays the interval end value.
Note

Use the AxisLabel.TextPattern property to format label text when the GridLayoutMode (IntervalNumericScaleOptions.GridLayoutMode, DateTimeScaleOptionsBase.GridLayoutMode or QualitativeScaleOptions.GridLayoutMode) property is set to GridAndLabelShifted.

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