Heat Map Widget

The Heat Map widget is a colorized grid chart that displays a central variable of interest across two-axis variables. In LogScale, this is typically the result of grouping on two categorical variables or binned numerical values.

See an example of how this widget may look like in Figure 168, “Heat Map Widget”.

Heat Map Widget

Figure 168. Heat Map Widget


Input Format

You can use the Heat Map widget to visualize results of the groupBy(), top(), bucket(), and timeChart() query functions. In all cases, the result needs to contain two grouping variables and a third variable with the aggregate result. Thus, for groupBy() and top() you need to specify two fields to group by, and for bucket() and timeChart() you need to specify a single field to group by along with the timestamp.

Example 1: Github Push Events

The Heat Map widget is typically well suited when there is an inherent ordering to both the axis variables and you want to have, for instance, an overview of how many events fall into each combination of those variables.

One example taken from a Github sample dataset is the push activity — at what times during a week are there most activities on Github based on push events.

logscale
type="PushEvent"
| dayOfWeekName := time:dayOfWeekName()
| dayOfWeek := time:dayOfWeek()
| hour := time:hour()
| groupBy([dayOfWeekName, dayOfWeek, hour])
| sort([dayOfWeek, hour], type=[number, number], order=[asc, desc], limit=200)
| drop(dayOfWeek)

This query creates dayOfWeek (and data of week number for sorting) and hour of day fields and computes a groupBy with the default _count aggregate function. Finally the query sorts the result such that both the Y-axis and X-axis are sorted. This type of query is best suited when all combinations of the grouping fields are present, otherwise the sorting of the heat map may be inconsistent.

Example 2: Response Time

The Heat Map widget can be used to detect how many events have a certain level of response time over time. The following query generates the result for a heat map showing this information.

logscale
case{
responseTime < 1
| responseBin := "< 1"
| responseBinNumber := 1;
responseTime < 5
| responseBin := "< 5"
| responseBinNumber := 2;
responseTime < 10
| responseBin := "< 10"
| responseBinNumber := 3;
responseTime < 50
| responseBin := "< 50"
| responseBinNumber := 4 ;
responseTime < 100
| responseBin := "< 100"
| responseBinNumber := 5;
*
| responseBin := ">= 100"
| responseBinNumber := 6;
}
| bucket(field=[responseBin, responseBinNumber])
| sort(responseBinNumber, limit=1000)
| drop(responseBinNumber)

The query first bins the response time and then computes an aggregated result using the bucket() function with the binned response time as the specified field. Finally, the query sorts the result by responseBinNumber such that the Y-axis of the map will be sorted.

Widget Properties

Use the widget's Edit Style panel or the brush icon on the right-hand side of the main Event List pane to configure the following properties.

  • Title

    The title of the widget as displayed in the dashboard.

  • Description

    The description of the bar chart. This is free form text supporting markdown syntax.

    This same description will appear in the dashboard as a tooltip by hovering over the question mark on top of the widget.

  • Layout

    • Gridlines

      Checkbox to enable/disable gridlines in the chart.

  • X-Axis

    • Max Label Length

      Slider to set the length of labels in the horizontal axis, in pixels. The chosen length affects the distance between labels.

    • Text Anchor

      Controls where the label is positioned under the grid. Options are:

      • Left

      • Center

      • Right

    • Angle

      Slider to modify the angle of the label in the horizontal axis.

    • Show Title

      Checkbox to show/hide the title assigned to the horizontal axis.

    • Custom Title

      Allows to change the default title of the horizontal axis and assign a preferred one.

  • Y-Axis

    • Max Label Length

      Slider to set the length of labels in the vertical axis, in pixels.

    • Show Title

      Checkbox to show/hide the title assigned to the vertical axis.

    • Custom Title

      Allows to change the default title of the vertical axis and assign a preferred one.

  • Legend

    • Location

      Sets the position of the legend in the chart. Valid options are:

      • Top

      • Right

    • Min Value

      Sets the minimum value of the legend range. If an input aggregate value is below the specified value, it will be mapped to the minimum color.

    • Max Value

      Sets the maximum value of the legend range. If an input aggregate value is above the specified value, it will be mapped to the maximum color.

    • Show Title

      Checkbox to show/hide the title assigned to the legend.

    • Custom Title

      Allows to change the default title of the label and assign a preferred one.

  • Tooltip

    Appears when hovering over a cell and shows the X-axis and Y-axis values together with the aggregate value of the cell.

    • Include Histogram

      Checkbox to show/hide a histogram in the tooltip. The histogram displays hovered columns as bar charts to reveal content.

  • Colors

    • Palette

      Allows to change the color of the grid; options are:

      • Teal Monochrome

      • Magenta Monochrome

      • Peach Monochrome

      • Blue Monochrome

      • Green Monochrome

      • Green Red Diverging

    • Reverse

      Checkbox to select/deselect the inverted colors option (all the colors are the opposite in the grid).