evselect supports the reading and writing of data subspace information into a data set, which allows one to track the filtering history of a file. A data set with data subspace information can be used as an input to evselect, in place of a filtering expression, using the parameter dssblock. evselect will also take the input filtering expression and convert it into a data subspace specification, which will then be written to all output files.
Not all possible filtering expressions allowed by selectlib can be converted to a data subspace specification. See the dsslib documentation for a detailed description of the capabilities of the data subspace parser.
The writing of data subspace information is enabled by default, and controlled by the parameter writedss. The data subspace also has a cleaning option, which will eliminate any components from the data subspace which do not select any events in the event list. This can result in the loss of important filtering information, and thus it is recommended that data subspace cleaning be used by experts only. The parameter for enabling data subspace cleaning is dssclean, and is set to false by default.
