Suspend the execution of an R code for a time interval

The Sys.sleep function allows to stop the execution of an R process for a time interval, in seconds. This is very useful when you run a for loop and you need to slow down the speed of the loop.

Syntax and use cases

The function takes a positive number as input which will be the number of seconds to suspend the execution of the code.

Sys.sleep(time)

This function has several use cases. Some of them are:

• When you are scraping a website or downloading files and you don’t want to overload the server.
• To delay the execution of some code.
• When you want to retry some code that failed after some time (e.g. a server is down and you need to wait some time until is up).
• When you are making API calls to a limited API (e.g. it admits X calls per hour).

Using Sys.sleep inside a for loop

Consider the following for loop that prints the execution time of each iteration:

for(i in 1:5) {
  
  # Start time
  start <- Sys.time()
  
  # Code
  
  # End time
  end <- Sys.time()
  
  # Time difference
  time <- end - start
  
  print(time)
  
}

Time difference of 2.861023e-06 secs
Time difference of 1.907349e-06 secs
Time difference of 1.907349e-06 secs
Time difference of 3.099442e-06 secs
Time difference of 9.536743e-07 secs

Each iteration takes almost no time to complete. However, if you want to stop the execution one second each iteration you can use Sys.sleep(1).

for(i in 1:5) {
  
  # Start time
  start <- Sys.time()
  
  Sys.sleep(1)
  
  # End time
  end <- Sys.time()
  
  # Time difference
  time <- end - start
  
  print(time)
  
}

Time difference of 1.003335 secs
Time difference of 1.012604 secs
Time difference of 1.014571 secs
Time difference of 1.028076 secs
Time difference of 1.027852 secs

Now each iteration takes around 1 more second to complete.

Using Sys.sleep inside sapply

You can also use the Sys.sleep function inside a sapply or a lapply function. In the following example we are pausing the execution 5 seconds between iterations.

sapply(1:5, function(i) {
  
  Sys.sleep(5)
  
  return(i)
  
})

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