Frequencies for first 10,000 rows of cityres variable in natlterr2001 dataset :

    City of |
  Residence |      Freq.     Percent        Cum.
------------+-----------------------------------
        000 |          9        0.09        0.09
        999 |      9,980       99.80       99.89
        ZZZ |         11        0.11      100.00
------------+-----------------------------------
      Total |     10,000      100.00

by Jean Roth , jroth@nber.org , 22 Dec 2015