Frequencies for first 10,000 rows of shipnum variable in natl1969 dataset :

   Shipment |
     number |      Freq.     Percent        Cum.
------------+-----------------------------------
         01 |      2,180       21.80       21.80
         02 |      2,342       23.42       45.22
         03 |      2,575       25.75       70.97
         04 |      2,364       23.64       94.61
         05 |        533        5.33       99.94
         99 |          6        0.06      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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