Frequencies for first 10,000 rows of ab_surf variable in natlterr2010 dataset :

 Surfactant |
        RFP |
631=f_ab_su |
     rfac R |      Freq.     Percent        Cum.
------------+-----------------------------------
            |      4,656       46.56       46.56
          N |      4,311       43.11       89.67
          U |        976        9.76       99.43
          Y |         57        0.57      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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