[R] R - Populate Another Variable Based on Multiple Conditions | For a Large Dataset

[Kevin Wamae]

I have a drug-trial study dataset (attached image).

Since its a large and complex dataset (at least to me) and I hope to be as clear as possible with my question.
The dataset is from a study where individuals are given drugs and followed up over a period spanning two consecutive years. Individuals do not start treatment on the same day and once they start, the variable "drug-admin" is marked "x" as well as the time they stop treatment in the following year.
There exists another variable, "study_id", that I hope to populate as can be seen in the dataset, with the following conditions:

For every individual
•    if the individual has entries that show they received drugs both on the start and end date (marked with the "x")
•    if the start of drug administration falls in month == 2 | 3 and end of administration falls in month == 2 | 4
•    then, using the date that marks the start of drug administration, populate the variable _"study_id"_ in all the rows that fall within the timeframe that the individual was given drugs but excluding the end of drug administration.
I have tried my level best and while I have explored several examples online, I haven't managed to solve this. The dataset contains close to 6000 individuals spanning 10 years and my best bet was to use a loop which keeps crushing R after running for close to 30min. I have also read that dplyr may do the job but my attempts have been in vain.

sample code
-------------------------------------------------------------------------------------------------------------------------------------------------------------------
individual <- unique (df$ID)  #vector of individuals
datalength <- dim(df)[1]      #number of rows in dataframe

for (i in 1:length(individual)) {
  for (j in 1:datalength) {
    start_admin <- df[(df$year == 2007] & df$drug_admin == "x" & c(df$month == 2 | df$month == 3),1]  #capture date of start
    end_admin <- df[(df$year == 2008] & df$drug_admin == "x" & c(df$month == 2 | df$month == 4),1]    #capture date of end

    if(df[datalength,1] == individual(i) & df[datalength,2] >= start_admin & df[datalength,2] < end_admin) {
      df[datalength,6] <- start_admin #populate respective row if condition is met
      }
    }
  }

-------------------------------------------------------------------------------------------------------------------------------------------------------------------

Above is the code that keeps failing..

Any help is highly appreciated....


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