Frequencies for first 10,000 rows of shipnum variable in natl1975 dataset :

   Shipment |
     number |      Freq.     Percent        Cum.
------------+-----------------------------------
         01 |      1,868       18.68       18.68
         02 |      2,139       21.39       40.07
         03 |      2,377       23.77       63.84
         04 |      2,346       23.46       87.30
         05 |      1,264       12.64       99.94
         99 |          6        0.06      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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