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9.3.8 Trellis Plot


Trellis plots or Trellis graphs (also sometimes termed "Trellis displays" or simply "Trellis") are a means of graphing multivariate data, as an array of M X N panels. As a simple example, two "primary variables" might be chosen to represent a common set of axes (repeated in each panel), against which all combinations of two categorical variables (termed "conditioning variables") are plotted. Each combination of categorical values is plotted as a separate panel.

Trellis plots example.png

In Origin terms, when your data includes a column of categorical data, or multiple columns characterizing some sort of nested sub-grouping of data, you might gain from plotting the data as a Trellis. Trellis plots were introduced in Origin 2017.

Creating a trellis plot

  1. Highlight one or more Y worksheet columns (or a range from one or more Y columns).
  2. Select Plot: 2D: Trellis.

This will open the plot_group dialog

Trellis 01.png

Since Origin 2018b, the Trellis plot supports more plot types: Stacked Column,Stacked Bar,100% Stacked Column and 100% Stacked Bar.

Trellis plot types 2018b.png

The Box Charts also supports a Trellis type arrangement. See Plotting Box Chart in Trellis, below.

The following quick example uses the dataset <Origin exe folder>/Samples/Statistics/LogRegData.dat, imported (File: Import: Single ASCII) using default settings. The dataset contains two columns of categorical data: Gender (Col(C)) and Career_Change (Col(D)). We are going to add one more categorical variable, City, and then plot this dataset in a Trellis.

  1. Click the Add New Columns button Button Add New Columns.png on the Standard toolbar to add an empty column to the right side of the sheet.
  2. Highlight cells 1 - 350, right-click and choose Fill: Arbitrary set of Text&Numeric Values and recreate these settings in the dialog box that opens:
  3. Trellis 16.png

  4. In the Long Name cell in the cities column, type Cities.
  5. Highlight Col(B) and from the menu, select Plot: 2D: Trellis Plot to open the plot_group dialog.
  6. Select Scatter for Plot Type. Under Variable for Separate Panels, click the triangle beside Horizontal and add Gender and Cities (in that order). For Vertical, select Career_Change.
    Trellis 18.png
    Click OK to create your Trellis.
    Trellis 17.png

Controlling the arrangement of horizontal and vertical panels

Method 1. Use the plot_group dialog's Variable for Separate Panels controls to determine the horizontal and vertical arrangement of panels
Trellis 02.png
Method 2. Use the Plot Details dialog Panel tab controls to re-arrange plots in panels after plotting
  1. In the left panel of Plot Details, highlight a data plot. The right panel will include a Panel tab.
    Trellis 03.png
  2. On this tab, you can re-arrange panels by size or by grouping column(s).
    • by size
      Trellis 04.png
    • by grouping column(s)
      Trellis 05.png
  1. Import the file <Origin exe folder>/Samples/Statistics/body.dat (File: Import: Single ASCII) and accept default settings. We are going to plot height vs. weight data, categorizing by age and gender, respectively.</li>
  2. Set height column as X by right clicking on it and selecting Set As: X.
  3. Highlight height and weight columns, and select Plot: 2D: Trellis to open the plot_group dialog.
  4. Under the Variable for Separate Panels branch, select the age column for Horizontal and the gender column for Vertical.
    Click OK to create your Trellis.
Trellis 06.png

Mapping color to data plots

Color-map plots to a specified column
  • In the plot_group dialog, specify the mapped color column in Variable to Color Data Points.

Or

  • In the Plot Details dialog, go to Symbol tab, set Symbol Color: By Points: Indexing/Color Mapping.
Color map plots to a color increment list
  1. In the Plot Details dialog, go to Symbol tab, set Symbol Color: By Points: Increment
    Trellis 07.png
  2. Go to Panel tab, you can increment plot colors within a panel or between panels.
    • within a panel
      Trellis 08.png
    • between panels
      Trellis 09.png

Wrapping panels

When you have many categories in a grouping column, the Trellis plot can become squeezed for space. The solution is to "wrap" panels, breaking a row or column of panels into multiple rows/columns.

  1. Double-click on a plot to open the Plot Details dialog.
  2. On the Panel tab, select the Wrap Panels if Columns/Rows Exceed checkbox and enter the desired number in the edit box.
Trellis 11.png

The following quick example uses one of the Learning Center sample OPJs.

  1. Choose Help:Learning Center... to open the Learning Center dialog.
  2. Select the Graph Sample tab on the left, and on the right select Trellis Plot from Samples in drop-down list.
  3. Double-click on the first cell of the second row to open the OPJ. Activate the workbook Book9. We are going to create a female vs. male Trellis categorized by years, and then wrap it to 3 X 2 panels.
  4. Right-click on column C and select Set As: X.
  5. Highlight column C and D, select Plot: 2D: Trellis to open the plot_group dialog.
  6. Select Scatter for Plot Type.
  7. Select column B for Variable for Separate Panels: Horizontal. Click OK to create a Trellis.
  8. Double-click on the scatter plot to open the Plot Details dialog. On the Panel tab, select the Wrap Panels if Columns/Rows Exceed checkbox and enter 3 in the edit box.
Trellis 12.png

Combining multiple panels into a single panel

  1. Create a set of categorized plots in multiple panels by the plot_group dialog.
  2. Double-click on the Trellis to open the Plot Details dialog. On the Panel tab, check Overlap Panels in the Horizontal Panel or Vertical Panel group.
Trellis 19.png

The following quick example uses one of the Learning Center OPJs.

  1. Select Help: Learning Center to open the Learning Center dialog. In this dialog, select Graph Sample in left panel, and then choose "Trellis Plot" from Samples in drop-down list.
  2. Double-click on the graph in the lower right corner, "Trellis - Overlap Panels with Multiple Categories Combination".
  3. Activate workbook Book8. We are going to plot a set of Line+Scatter curves, grouped by columns Location and Treatment, in one panel.
  4. Highlight column C and select Plot: 2D: Trellis Plot to open the plot_group dialog.
  5. Select Line+Symbol for Plot Type.
  6. Select column F and G for Variable for Separate Panels: Horizontal. Click OK to create the Trellis.
  7. Double-click on the Trellis to open the Plot Details dialog. On the Panel tab, check Overlap Panels in the Horizontal Panel group.
  8. Go to Symbol tab, set Symbol Color: By Points: Increment from: to red color.
  9. Go to Panel tab. Select Between Panel from the Increment on Panel group.
Trellis 10.png

Plotting box chart in trellis

  1. Create a box chart
  2. Double click on it to open the Plot Details dialog. Specify the categorical column(s) on the Panel tab to seperate the boxes into panels accordingly.

The following quick example uses one of the Learning Center OPJs.

  1. Select Help: Learning Center to open Learning Center. In the dialog that opens, select Graph Samples tab on the left, and then choose "Trellis Plots" from drop-down list on the top.
  2. Double-click on the graph to open sample "Trellis Plots - Box Charts".

The workbook Trellis Plots - Box Charts contains sales data of two automobile brands: BMW and Ferrari. We are going to plot them as a box chart, seperated the boxes into different panels by their regions, and then show Mean line for each region.

  1. Create a box chart. Highlight col(C) and col(D) in Sheet1, and then select Plot: 2D> Box> Grouped Box Charts - Raw to create a box chart.
  2. Seperate boxes to 3 penals accroding to different regions. Double click on the box to open the Plot Details dialog. Activate Panel tab. Select By Column(s) for Horizontal Panel and select B(Y):Region for Column(s).
    Trellis 20.png
  3. Add a Mean line for each panel. Double click Y axis to open the Axis dialog. Activate Reference Lines tab. Add mean line as follow
    Trellis 21.png


    Trellis 22.png

Axis Display

Each panel in a Trellis plot shares a common set of axes with other panels in the Trellis. Note that these axes are not customized using the two dialog boxes that we have previously discussed: the plot_group dialog and Plot Details.

Axis customizations are made via the Axis dialog box. In this section, we will point out how a few small axis customizations might make your graph more readable.

Some axis customizations can be done using Style and Format toolbar buttons. For instance, you can select (single-click) tick labels and use the Italics button Italics.png to italicize tick label text; or use the Line/Border Style Lineborder style.png or Line/Border Width Button Border Width.png controls to set line styles and weights.

To open the Axis dialog box:

  1. Double-click on the axis or axis tick labels.

or

  1. With the graph active, choose Format: Axes: X/Y/Z Axis, from the main menu.

Grid Lines

In the following example, we have barley varieties on the vertical axis and yields by location on the horizontal axis. Note how enabling grid lines for the vertical axis makes the plot easier to read. Trellis axis grids enabled.png

In the previous example, we enabled Major Grid Lines to connect tick labels to plotted data. In the next example, we enable Minor Grid Lines to separate tick labels and plotted points from adjacent labels and points.

Trellis axis grids minor.png

Tick Label Tables

Tick Label Tables offer a way to create multi-level labeling of graph axes, typically in plots of categorical data. Tick Label Tables are often used in box charts and column/bar charts and since Origin 2018b, have been available in Trellis plots.

Trellis tick label tables.png

To open the Axis dialog box to Tick Label Table controls:

  1. Double-click on the Tick Label Table or choose Format: Axes.
  2. Click on the Tick Labels tab and use Format and Table sub-tab controls to configure the tick tables.

For more information on using Axis dialog box controls to configure Tick Label Tables, see the Axis dialog Tick Labels tab.

Panel Banner String Customization

By default, the Trellis Panel Banner will display the categories of the associated categorical variable but you do have control over what is displayed in the banner. For instance, in the following example, you can see that the default banner display on the left shows an alphanumeric string (A386, C334).

This won't mean much to those who are not familiar with your data. One alternative, of course, is to add a graph legend or text label to explain but you can also modify the string that the banner displays. In this case, we change from the default option <Panel1> which displays just the category, to <Panel1, @LA>=<Panel1> which changes the string to the form "Column Long Name = Category".

Trellis modify panel banner string.png

Note that clicking the arrow button Button Arrow in Legend Tab.png to the right of the String box produces a flyout menu with suggestions for building your string.

For a complete list of string possibilities, see the Complete List of @Options in the LabTalk Help file.

Note: In this section, we have talked about Tick Label Tables and Panel Banners. They are similar in appearance but note that Panel Banners are specific to Trellis plots, while tick label tables are more general and can be used in Box charts, Column/Bar charts, etc. Both can be customized via the graph's Axis dialog box.

Other Tick Label Customizations

Long text strings on tick labels necessitate some sort of adjustment and apart from changing font size, note that you can (a) wrap tick labels or you can (b) rotate tick labels. Both adjustments can be made using controls on the Format tab of the Axis dialog box.

Trellis axis label rotation.png
  1. Click on the Tick Labels tab and use Format sub-tab controls to set Font, Size, Rotate (deg.) or Wrap Text.

Reference

  1. Trellis Display: Interview. Bell Labs web page: http://ect.bell-labs.com/sl/project/trellis/interview.html.
 

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