Dear Group,

I have the following dataset:
   ID REPI     DV CONC SS
    1    1 156.84  116  0
    1   2 146.56  116  0
   1    3 115.13  116  0
   1    4 207.81  116  0
  1    5 129.53  116  0
  1    6 151.48  116  0
  1    7 158.95  116  0
  1    8 192.37  116  0
  1    9  32.97  116  0
  1   10 151.66  116  0

I want to calculate the percentile of each CONC within ID=i and add as a
column "Percentile".  I got some help from R-tutorial on percentile but I
am not able loop the function to calculate percentile/individual.  So, I
want the calculation to include only the ID=1 DVs to calculate the
pecentile of conc=116.  I truly appreciate your help.

Regards,
Ayyappa

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