st: Generate new variable "by" question

["Dale Steele" <Dale_Steele@brown.EDU>]

minus the value of response when resistnc is 0.  Seems like I should use the
"by" command, but I'm having a hard time creating working code. My efforts
thus far ...

 by idnum: generate cresponse = response - (the value for response given
resistnc = 0 for each idnum)

. list idnum resistnc response

         idnum   resistnc   response
  1.       401          0        .14
  2.       401        2.5       2.42
  3.       401          5       3.76
  4.       401         10       4.74
  5.       401         20       7.88
  6.       401         30       8.52
  7.       402          0         .4
  8.       402        2.5       1.46
  9.       402          5       1.58
 10.       402         10       4.08
 11.       402         20          6
 12.       402         30       8.94

Thanks...
    Dale Steele


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