Using BY-Group Processing

To subset data into disjoint subsets defined by one or more BY variables, follow these steps:

1. On the Graph menu, select a plot type.

   IML Studio displays the dialog box for the plot type.

2. In the Variables tab, select the plot variables.
3. Click the BY Variables tab.
4. Select one or more nominal variables and click Add BY.

   IML Studio uses the values of the BY variables to split the data into disjoint subsets.

5. Click the BY Options tab and specify options for the plots.
6. Click OK.

IML Studio splits the data into disjoint subsets, called BY groups. Each BY group is plotted on a separate plot. The BY groups are, by definition, mutually disjoint. Consequently, these plots are not dynamically linked to each other.

The dialog box for creating a plot contains the following tabs:

• BY Variables

  This tab enables you to choose the BY-group variables. The values of the BY-group variables define the BY groups.

• BY Options

  This tab enables you to set options used to subset the data and to create the BY-group plots. The tab provides the following controls:

  Individual plot windows

  This check box specifies whether to display plots on the screen. The Layout drop-down list specifies how plots are arranged on the screen.

  Output document

  This check box specifies whether to copy plots to the output window. The Graphic type drop-down list specifies the image type for plots copied to the output window. For a discussion of image types, see Exporting Plots: Graphics File Formats.

  Files

  This check box specifies whether to write plots to files on the client (or a networked drive).

  Directory

  This edit box specifies the directory for writing plots to files.

  Filename root

  This drop-down list specifies the prefix used for writing plots to files. The plots are named Root001, Root002, etc. The suffix of each file corresponds to an enumeration of the BY groups. Existing files with the same name are overwritten.

  File type

  This drop-down list specifies the image type for plots written to files. For a discussion of image types, see Exporting Plots: Graphics File Formats.

  Data order determines BY groups

  This option corresponds to the NOTSORTED option in the BY statement in SAS procedures. If this option is selected, then no sorting is done prior to forming the BY groups. If this option is not selected, then the BY variables are internally sorted and the BY groups consist of observations corresponding to the unique values of the BY variables.

  Individual plots can reference all variables (slow)

  If this option is selected, then all variables are copied when forming BY groups. If this option is not selected, then the BY groups contain only the variables specified on the Variables and BY Variables tabs. This option is available only when Individual plot windows is selected.

  Set uniform axis range for interval variables

  If this option is selected, then the axes of interval variables are set to a common range. If this option is not selected, each axis is scaled individually according to the data in each BY group. This option is ignored for a rotating plot and for nominal axes. This option does not affect the frequency axis for histograms or bar charts.

Details of BY-Group Processing

When you create BY-group plots, the following steps occur:

1. A new variable, _ObsNum_, is added to the current data table.
2. The observations corresponding to each BY groups are identified.
3. The observations in each BY group are copied to a new DataObject. The variables that are copied depend on the Individual plots can reference all variables option on the BY Options tab. Observation properties (such as the color and shape of markers) are also copied to each BY group.
4. The plots are created.

The BY-group plots are not dynamically linked to the original data. Consequently, selections made to the original data are not reflected in the BY groups. However, you can use an action menu to select observations in the original data that correspond to selected observations in a BY-group plot. Press the F11 key to display the action menu in a BY-group plot. When you select the action menu item, IML Studio looks at the values of the _ObsNum_ variable for the selected observations. IML Studio then selects observations in the original data that contain the same values of _ObsNum_.

Using the action menu to select observations is a cumulative process: if an observation in the original data was selected prior to this action, it remains selected after the action. You can clear selections in the data table the usual way: press the ESC key or click in the upper-left cell of the data table.