[R] create a dummy variables for companies with complete history.

[giacomo begnis]

Hi, I have a dataset  (728 obs) containing three variables code of a company, year and revenue. Some companies have a complete history of 5 years, others have not a complete history (for instance observations for three or four years).I would like to determine the companies with a complete history using a dummy variables.I have written the following program but there is somehting wrong because the dummy variable that I have create is always equal to zero.Can somebody help me?Thanks, gm

z<-read.table(file="c:/Rp/cddat.txt", sep="", header=T)
attach(z)
n<-length(z$cod)  // number of obs dataset

d1<-numeric(n)   // dummy variable

for (i in 5:n)  {
   if (z$cod[i]==z$cod[i-4])             // cod is the code of a company             { d1[i]<=1} else { d1[i]<=0}          // d1=1 for a company with complete history, d1=0 if the history is not complete  }d1
When I run the program d1 is always equal to zero. Why?
Once I have create the dummy variable with subset I obtains the code of the companies with a complete history and finally with a merge  I determine a panel of companies with a complete history.But how to determine correctly d1?My best regards, gm



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