Frequencies for first 10,000 rows of shipnum variable in natl1970 dataset :

   Shipment |
     number |      Freq.     Percent        Cum.
------------+-----------------------------------
         01 |      2,173       21.73       21.73
         02 |      2,599       25.99       47.72
         03 |      2,672       26.72       74.44
         04 |      2,317       23.17       97.61
         05 |        239        2.39      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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