A: This can be done by using Filters in the Attribute Manager to subset the data. Applying Filter on your data uses the same mechanism as applying colour/shape/size attributes. Functions such as summary statistics, calculating ranked percentiles, data leveling, clustering, etc, are calculated on the filtered data only. Please refer to the ioGAS Help file for more details.
Prior to ioGAS 6.0, the only way to do this in ioGAS is by making the desired selection, and turn off the visibility for all the other data. Then use the Edit>Remove Invisible Rows menu options to physically remove the invisible data points from view. The values of the other colour, shape, size attributes will then be relevant to just this subset of data. Although the warning messages says the removal is permanent, you can always use the File>Revert menu option to get all of the data points back again. Note that saving the session will remove the invisible data permanently.