We broached the subject of creating an index file in previous chapters. In this section, we will describe how the indexes are stored and retrieved. The index file consists of entries that are organized hierarchically and connected by pointers, all of which are maintained by SAS. The lowest level in the index file hierarchy consists of entries that represent each distinct value for an indexed variable, in ascending value order. Each entry contains the following information:

  • A distinct value
  • One or more unique record identifiers (referred to as a RID) that identify each observation that contains the value

If we created an index for the City variable using the AC dataset in the mismatch dataset, we would have an index file with entries ...

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