Frequencies for first 10,000 rows of ab_surf variable in natlterr2005 dataset :

 Surfactant |
          R |      Freq.     Percent        Cum.
------------+-----------------------------------
            |      6,255       62.55       62.55
          N |      3,695       36.95       99.50
          Y |         50        0.50      100.00
------------+-----------------------------------
      Total |     10,000      100.00

by Jean Roth , jroth@nber.org , 22 Dec 2015