Frequencies for first 10,000 rows of ab_surf variable in natl2014 dataset :

 Surfactant |
      Y Yes |      Freq.     Percent        Cum.
------------+-----------------------------------
          N |      9,721       97.21       97.21
          U |        269        2.69       99.90
          Y |         10        0.10      100.00
------------+-----------------------------------
      Total |     10,000      100.00

by Jean Roth , jroth@nber.org , 15 Jun 2016