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HistogramChart

A HistogramChart is a type of graph that represents the distribution of numerical data. It’s constructed by dividing the entire range of values into a series of intervals—known as bins and then counting how many values fall into each interval. The bins are typically of equal size and are adjacent to each other, with no gaps. Each bin is represented by a bar, where the height of the bar reflects the frequency or count of data points within that interval

Overview Properties

Import

import { HistogramChart } from '@dynatrace/strato-components-preview/charts';

Use cases

The HistogramChart expects a data structure composed of an array of bins, a name as a string, an optional unit as a string or Unit and optional color as a string.

Each bin represents a continuous range of values. A bin is defined by two key parameters: the range (from and to), which determines its width, and the count or frequency (value), which determines its height.

 {
    name: 'Series 1',
    bins: [
      {
        from: 0,
        to: 10,
        value: 0,
      }
    ]
 }

Learn more about the data format here.

Uneven Bin Widths

The HistogramChart accommodates uneven bin widths, providing a clearer representation of the data. Each bin corresponds to a specific range of values and these ranges can vary from one bin to another.

Overlapped and Stacked Bins

In some instances of the HistogramChart, when bins are not perfectly aligned along the x-axis, the resulting bars may overlap. Conversely, if a bar aligns perfectly, it will be stacked.

ℹ️ If you are interested in how to prepare your data for passing it to the this article might

Size

By default, the chart will use all the available container size up to a maximum height of 300 pixels. This maximum height can be changed by providing a value in the height prop of the HistogramChart. If a number is passed to this prop without any unit specified, it will be treated as px.

Series actions

A series action is a creator-defined interaction with a given data point in the chart. Basic interactions include copying a series name and inspecting the underlying data of a data point. Series actions support both synchronous and asynchronous callbacks. In order to enable chart interactions, the ChartSeriesAction subcomponent needs to be appended within the HistogramChart. More subcomponents can be added within this component, for instance ChartSeriesAction.Item, where you can provide a custom action that will appear in the legend menu. That action can execute any custom logic in its onSelect callback or get disabled via a disabled prop. Intents could be added as part of the series action as well with ChartSeriesAction.Intent.

Change the chart color/s

The HistogramChart provides a set of predefined color palettes and it also accepts custom color palettes. See coloring for more details.

Apart from all these options for providing a color palette, the HistogramChart also offers the ability to override colors for specific series. When a color override is specified, it takes precedence over the color that would otherwise be assigned from the color palette. However, it does not affect the colors assigned to other series. This allows for fine-grained control over the appearance of individual series within the chart. The desired color should be specified in the color prop of a specific series.

Value representation

By default, values within a chart are displayed as is - with their absolute value (e.g. 3.14 kB). However, this can be changed so that instead of absolute values, relative values are used. Relative values indicate the proportion that a given dimension contributes to the sum (100%) of a given histogram bin. The valueRepresentation prop can be used to change this behavior. For series with only a single dimension, the relative value is based on the maximum value within the given series.

Legend

The purpose of the legend is to provide additional identifying information for the chart, without needing to interact with the legend directly.

Visibility

The legend of the HistogramChart is shown by default. In order to hide or show the legend, you need to set the value of legend.hidden on the subcomponent.

Position

By default, the position of the legend of the HistogramChart is set automatically. This option prioritizes the legend placement to the right of the chart area. When the chart width is reduced, the legend is repositioned to the area beneath the chart. It is also possible to explicitly set the chart's legend position to right or bottom with the position prop.

Legend ratio

By default, the legend occupies 25% of the container width, in the case where the legend is positioned on the right and 25% of the container height if the legend position is on the bottom.

It is possible to override the default legend ratio by setting a custom percentage value for the ratio prop. The expected value is in the range of 5-80. Values out of expected ranges will roll back to the default legend ratio.

Chart Interactions

The HistogramChart provides various interactions (e.g. zoom-x, zoom in, zoom out, and pan) that can be optionally enabled. See chart interactions for more details.

Axes

To configure the axes of the HistogramChart, the HistogramChart.XAxis and HistogramChart.YAxis subcomponents can be added. The label property sets the axis label. Axis scale boundaries can be set with the min and max props. Both XAxis and YAxis supports linear and log scales.

Both HistogramChart.XAxis and HistogramChart.YAxis subcomponents also support data-max in the max property and data-min in the min property. These special values allow for granular control over the Y-axis scale boundaries. By default, the auto value is used for both min and max properties. The auto mode automatically determines both the minimum and maximum values of the Y-axis scale based on the data in the chart (similar to data-min and data-max) and sets the Y-axis baseline to zero.

Multiple Y-axes

The HistogramChart supports multiple Y-axes. HistogramChart.YAxis provides a position property which can be set to either left or right.

When you specify multiple Y-axes, the chart automatically assigns data series to Y-axes based on the unique units of the data. The first unique unit is assigned to the left Y-axis, and the second unique unit to the right Y-axis. Note that any additional data series with different units from those already used will not be displayed.

Currently, it's not possible to assign data series to specific Y-axes, nor is it possible to use the same unit for both Y-axes.

Tooltips are used to display additional detailed information about a selected data point and can be enabled by adding the HistogramChart.Tooltip subcomponent. The tooltip variant defines whether the tooltip should contain data points from all bins (shared) for the selected bin, or just the closest one (single). The seriesDisplayMode prop can be used to define whether the tooltip should be comprised of a single line of information or multiple lines.

The sequence of the input data in the chart determines the arrangement of the tooltip series.

Single

Shared

Formatter

The unit for the HistogramChart, by default, will be appended to the specified value. There are two other options in the formatter that allow for greater customization. The first option enables you to prepend the unit to the value, while the second option enables you to ignore the original unit and append a custom string instead. Additionally, there is a custom formatter option available to allow you to change the input unit to one of your choice, e.g.: if the input unit is bits, you are able to switch and display the unit as bytes, correctly formatted. The formatted value is applied in the axis ticks, as well as in the tooltip and the axis magnifier. The use cases below outline each of these scenarios.

The precision of the formatter will adapt automatically based on the data decimals if there is no precision configuration from the custom formatter option.

Annotations

Annotations are used to visualize specific events or contextual notes on the HistogramChart in the form of markers placed in the bins position.

The marker represents an annotation at a certain bin. They can be either a value (a certain number) or a range (from-to object), depending on the data provided to the Annotation. Annotations within the same bin are grouped together under a single marker that displays the number of grouped annotations. Markers can be displayed on a single or multiple tracks. When there are more than three tracks, an overflow scroll is applied.

Add annotations to the chart

In order to visualize annotation data inside the HistogramChart, a HistogramChart.Annotations component should be initialized. This component should have at least one track, that contains a marker component per annotation data point.

An annotation data point should contain the from-to bin information (value: {from: number, to:number}) or a certain point (value: number), an optional symbol, title, and description, which will be displayed in the tooltip.

Marker content

When the symbol is provided, it will become the marker content by default. When not, the title will be shown as marker content.

In case the content of the marker is bigger than the size of the marker (bin size in Histogram), it will expand to fit all the content inside, decoupling from the original scale. In these particular cases, it is encouraged to use the indicators, which will represent the real size of the bin.

Visual customization

Tracks and markers support visual customization in order to differentiate various types of annotations.

It's possible to set custom colors on both the track (to be applied to all markers) and the marker level by using the color property on the respective component. A marker's custom color has precedence over track's. This color can be set to any Design System color token, as well as any rgb, hex or CSS color.

The symbol property allows you to apply an icon, emoji, single letter, glyph, or Design System icon to either an individual marker or to an entire track. When applied to a track, this symbol will be used as the default.

When markers partially overlap one another, the order of the annotations defines which marker is displayed on top. Value annotations are always displayed above Range-based ones. It's also possible to customize the marker display order, by using the priority property. The higher the value of the priority property, the higher precedence the marker has. The priority property also affects the color of markers i.e. within a group, the color of the marker with the highest priority will be applied to the group.

It's possible to assign a label to a track using the label property. Be aware that labels are hidden by default. To show a track's label, the showLabels property has to be applied to the HistogramChart.Annotations component.

Visibility

An entire track can be hidden by adding the hidden property to the HistogramAnnotations.Track component. The same configuration can be applied to a marker, by setting the hidden property on the HistogramAnnotations.Marker component.

When hovering a marker (with the cursor), an annotation indicator appears over the chart area. The indicator's visibility can be customized on either a track or marker level by using the indicatorsDisplay property:

With the auto option, the default behaviour is applied - indicators appear on hover.
The always option sets indicators to always be visible within the chart area, regardless of the hovering behavior.
The never option sets indicators to never be visible.

The Annotations supports both default and custom tooltips for annotations. This allows creators to provide additional detailed information about specific datapoints or events in the chart.

See Annotations Tooltip for more

Thresholds

Thresholds are used to mark meaningful ranges or values on a HistogramChart and they add contextual information to a numerical axis. There are two variants of thresholds:

a specific point represented on the Y-axis and a line across.
a range - or filled area - represented by a pill on the Y-axis and a band across.

Point and Range

Both point and range can be represented by static or dynamic data sources. A static data source has a single value representing a point or a single key-value pair representing a fixed range. A dynamic data source has a data array containing more than one value or various key-value pairs.

There are three different types of threshold markers:

Range filled, where the value range is defined in order to display the threshold band. The upper and lower lines are not drawn unless the pill is hovered.
Range stroke-only variant, where a value range is defined in order to display the threshold band represented by upper and lower dashed lines. The upper and lower lines become continuous lines when the pill is hovered.
Point, where only one value is required to display the threshold. It's represented by a dashed line and when the point is hovered the line becomes a continuous line.

Dynamic Point

Dynamic Range

Dynamic Range Stroke Only

There is no limit defined for the number of threshold ranges or points that can be used in a single HistogramChart.

By default, thresholds are positioned on the left axis and with the use of the position prop, we can place thresholds on the right axis or on both, as depicted below.

Left Axis

Right Axis

Dual Axis

Error state

The ErrorState subcomponent is responsible for handling errors in a graceful manner, ultimately improving the overall user experience. Its primary function is to catch any errors that may occur with the data and display a fallback UI instead of crashing the entire application. The fallback UI occupies the full width and height of the chart, ensuring that users are still provided with a meaningful interface even in the presence of errors.

The ErrorState subcomponent offers a versatile feature that enables it to handle both default and custom error messages. You can provide a custom message through the ErrorState subcomponent, which will then override the default error message. This flexibility allows developers to tailor error messages to their specific needs and requirements, ensuring a more personalized and informative user experience.

The ErrorState subcomponent provides the flexibility to format custom error messages using HTML, which allows for enhanced customization and adaptability in presenting error information. Furthermore, it is possible to incorporate the original thrown error within your custom error message, ensuring that users receive comprehensive and relevant information when an error occurs.

EmptyState

The EmptyState subcomponent serves as a fallback when there is no data available to display in a chart. Its purpose is to provide a user-friendly way of informing the user about the current situation. When there is no data, a fallback UI is displayed occupying the full width and height of the chart, along with a default message.

A feature of EmptyState is its ability to handle custom messages. It provides the flexibility to format custom messages using HTML, which allows for enhanced customization and adaptability in presenting error information.

Loading

The loading prop is a boolean value that can be passed to the HistogramChart component to control its loading state. When the loading prop is set to true, the loading indicator appears in the middle of the chart plot to inform the user that the component is currently fetching or processing data. When the loading prop is set to false, the component should display its regular content.

Download data as CSV

The HistogramChart component supports download data in CSV format using a toolbar button. To enable this feature, a ChartToolbar subcomponent with ChartToolbar.DownloadData inside of it must be provided to the HistogramChart component. On click of the download button, raw data will be downloaded as a CSV file.

The CSV file contains the following columns:

name - the name of the series
unit - the unit of the series
from - the start of the bin range
to - the end of the bin range
value - the value of the bin

It's also possible to programmatically trigger the download of the CSV file by calling the downloadData method on the HistogramChart instance reference.

Intent options

The HistogramChart supports intent options in the toolbar. The intents appear in the toolbar's dropdown menu, allowing users to perform actions such as sharing a chart or viewing data in another application.

To add intent options to a HistogramChart, use the HistogramChart.Intent subcomponent:

Intent properties

payload: An object containing the data to be passed to the target app. The structure depends on the target application's requirements.
options: Configuration options for the intent.
keyProperties: Array of properties that should be included as keys in the intent.
recommendedAppId: Suggested target application ID.
recommendedIntentId: Suggested intent ID.
responseProperties: Array of properties to be included in the response.
icon: Optional custom icon to be displayed next to the intent option.
onResponse: Optional callback function that is called when a response is received from the target app.

Examples

The following examples demonstrates different intent options in HistogramChart:

Styling

The HistogramChart also accepts custom styling, which can be set using the props className and/or style as in a regular html element.

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