At least one feature layer must be loaded into ArcMap in order to use this
tool. If your feature layer is an event theme (points) and you are experiencing
problems, try making it a shapefile and trying again (right click on the
event theme in the Table of Contents, select Data, then Export Data).
Add/update a RNDSEL field.
The program will create a new field called RNDSEL and for all the randomly selected
features will assign a value of 1. All unselected features have a value of 0. If the
field already exists it is deleted and re-created. If you receive an error message
regarding permissions or access to the table, it is likely that you do not have
permission to modify this feature layer, or that it is already being edited elsewhere.
Saving the selection as a new feature layer.
When features are selected you can easily save those selected features to a new
feature layer by right clicking on the layer in the ArcMap Table of Contents,
selecting Data, then Export Data.
Switching the selection.
To switch the selection (all currently unselected features become selected and
vice versa), open the attribute table, click on Options, and select Switch Selection.