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UNIQUE: Stata module to report number of unique values in variable(s)


  • Tony Brady



The command unique without a by reports the number of unique values for the varlist. With a by it does the same, but also creates a new variable (_Unique by default but can be named in the gen option). This new variable contains the number of unique values of the varlist for each level of the by variable. The new variable is coded missing except for the first record in each group defined by the levels of the by variable. The command is useful for exploring data where the records refer to more than one level, for example longitudinal data where each record refers to a visit by a subject.

Suggested Citation

  • Tony Brady, 1998. "UNIQUE: Stata module to report number of unique values in variable(s)," Statistical Software Components S354201, Boston College Department of Economics, revised 15 Jul 2018.
  • Handle: RePEc:boc:bocode:s354201

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