How to create a “conditional” variable in R?

Question

I want to create a conditional dummy variable. Assume that I have a dataset that looks something like this:

Subject Year    X   X1
   A    1990    1   0
   A            


        

Answer 1

How about this?

data$cX1 <- do.call("c",tapply(data$X1, data$Subject, FUN = function(x){
  nx=length(x) #i=1
  sx=c()
  if (nx<5) sx[1:nx]<-sum(x[1:nx]) else
  for(i in 1:nx)sx[i]<-sum(x[i:min(i+5-1,nx)])
  sx
},simplify = T))

data$Q1to3_noX1f2<-ifelse(data$Q1to3==1 & data$cX1==0,1,0)