How can I add the date of the data that satisfies a condition in ifelse in R?

Question

I need to date and time of the data that satisfies a condition in ifelse.

Glucose_4h <- character()
for(i in 1:96){
A <- unlist(difftime(Time_Meal[i], Time_Glucose[1:15372], units="mins"))
B <- ifelse(as.numeric(A)>0 & as.numeric(A)<5.0, "Inc_G","Exc_G")
Glucose_4h <- c(Glucose_4h,B)
}

In this code I also need which Time_Glucose satisfied the condition Could you help me about this?

Answer 1

So you need the values of Time_Glucose where Glucose_4h is equal to "Inc_G"? In your example B will always be 15372 long (the length of Time_Glucose. You could then capture that along with what you're currently doing:

res <- NULL
for(i in 1:96){
  A <- unlist(difftime(Time_Meal[i], Time_Glucose[1:15372], units="mins"))
  B <- ifelse(as.numeric(A)>0 & as.numeric(A)<5.0, "Inc_G","Exc_G")
  res <- rbind(res, data.frame(obs = i, Glucose_4h = B, Time_Glucose = Time_Glucose))
}

Then, if you only want the ones where Glucose_4h == "Inc_G", you could do the following:

res[which(res$Glucose_4h == "Inc_G"), ]