Frequencies for first 10,000 rows of shipnum variable in natl1971 dataset :

   Shipment |
     number |      Freq.     Percent        Cum.
------------+-----------------------------------
         01 |      2,416       24.16       24.16
         02 |      2,564       25.64       49.80
         03 |      2,715       27.15       76.95
         04 |      2,295       22.95       99.90
         99 |         10        0.10      100.00
------------+-----------------------------------
      Total |     10,000      100.00

by Jean Roth , jroth@nber.org , 3 Jan 2016