Activate/Deactivate a Loop in R

Question

I am trying to write a function to iterate over two variables (i.e. region and event). However, sometimes I need to apply the function to analyse the data of each whole region without dividing it into events.

I wrote the following code:

myfunction <- function(a, b, c, events_included = FALSE){
  for(region in c("A1", "A2", "A3", "A4")){
    for (event in 1:30){


      # The main code (tweaked to deal with the both cases in
      # which events_included = FALSE and TRUE).

    }
  }
}

I wonder if there is a way to deactivate the second loop (i.e. event) if the variable events_included = FALSE.

@cory Thank you for your suggestion. However, this would force me to write two similar blocks of code one for each case. My main code is already big and I do not want to copy-paste it into two blocks. I hope that I make sense to you. — MoMo, Apr 24 '19 at 20:31
You've got two people confused now, maybe it's time to clarify the question. — cory, Apr 24 '19 at 20:32
It's easier to help you if you include a simple [reproducible example](https://stackoverflow.com/questions/5963269/how-to-make-a-great-r-reproducible-example) with sample input and desired output that can be used to test and verify possible solutions. I'm not sure I understand the argument for duplicating code. Just write a function and call that function when you need to. — MrFlick, Apr 24 '19 at 20:33

Hector Haffenden · Answer 1 · 2019-04-24T20:36:59.630

Try this, using an if statement. You could put the if statement outside the loop, so it only checks once, this will speed up your code depending on the number of regions then you can just copy the code over...

myfunction <- function(a, b, c, events_included = FALSE){
  if (events_included){
    for(region in c("A1", "A2", "A3", "A4")){
      for (event in 1:30){
        # The main code (tweaked to deal with the both cases in
        # which events_included = FALSE and TRUE).
      }
    }
  } else {
    for(region in c("A1", "A2", "A3", "A4")){
        # Just region
    }

  }
}

Edit

If you don't want to have to copy the code twice, just add the if statement after the region for loop, but this will be a bit slower as for every region, an if statement will been to be checked....

myfunction <- function(a, b, c, events_included = FALSE){
  for(region in c("A1", "A2", "A3", "A4")){
    if (events_included){
      for (event in 1:30){
        # The main code (tweaked to deal with the both cases in
        # which events_included = FALSE and TRUE).
      }

      # Put region stuff here
    }
  }
}

If again, this forces you to copy code twice, if your region code is embedded with you events code, move the if statement inside the events for loop... etc...

Thank you for your suggestion. However, this would force me to write two similar blocks of code one for each case. My main code is already big and I do not want to copy-paste it into two blocks. I hope that I make sense to you. — MoMo, Apr 24 '19 at 20:29
See edit, just moved the if statement @DrMo hope this helps :) — Hector Haffenden, Apr 24 '19 at 20:31

MoMo · Accepted Answer · 2019-04-24T23:15:22.973

I think that I found a solution to the issue by allowing the second loop to do only one iteration. I have added if (events_included == FALSE & event > 1) break to my code as shown below:

myfunction <- function(a, b, c, events_included = FALSE){
  for(region in c("A1", "A2", "A3", "A4")){
    for (event in 1:30){
      if (events_included == FALSE & event > 1) break


      # The main code (tweaked to deal with the both cases in
      # which events_included = FALSE and TRUE).

    }
  }
}

The main code is already tweaked to work with both cases so there is no problem in that regard.

Please let me know if there is any problem with my reasoning. And sorry because I did not explain the issue clearly.

Activate/Deactivate a Loop in R

2 Answers2