Frequencies for first 10,000 rows of ab_surf variable in natlterr2015 dataset :

 Surfactant |
      Y Yes |      Freq.     Percent        Cum.
------------+-----------------------------------
            |      1,078       10.78       10.78
          N |      8,759       87.59       98.37
          U |         94        0.94       99.31
          Y |         69        0.69      100.00
------------+-----------------------------------
      Total |     10,000      100.00

by Jean Roth , jroth@nber.org , 20 Oct 2016