Frequencies for first 10,000 rows of shipnum variable in natl1974 dataset :

   Shipment |
     number |      Freq.     Percent        Cum.
------------+-----------------------------------
         01 |      1,953       19.53       19.53
         02 |      2,305       23.05       42.58
         03 |      2,238       22.38       64.96
         04 |      2,248       22.48       87.44
         05 |      1,252       12.52       99.96
         08 |          3        0.03       99.99
         99 |          1        0.01      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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