Frequencies for first 10,000 rows of ab_surf variable in natl2015 dataset :

 Surfactant |
      Y Yes |      Freq.     Percent        Cum.
------------+-----------------------------------
          N |      9,848       98.48       98.48
          U |        106        1.06       99.54
          Y |         46        0.46      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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