Frequencies for first 10,000 rows of ab_surf variable in natlterr2009 dataset :

 Surfactant |
        RFP |
631=f_ab_su |
     rfac R |      Freq.     Percent        Cum.
------------+-----------------------------------
            |      2,449       24.49       24.49
          N |      7,427       74.27       98.76
          U |          2        0.02       98.78
          Y |        122        1.22      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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