TryCatch

So the tryCatch function in R allows you to try run piece of code and if it gives a warining or error, to do something else instead of crashing. Lets take this example:
do_calculation<-function(){
  int<-sample(c(-1,1),1)
  sqrt(int)
}
​
x = c()
for (i in 1:10){
  x<-c(x,do_calculation())
}
​
sum(x)
We have a function do_calculation that returns the quare root of some number. It will randomly sample either 1 or -1. Trying to return the square root of -1 will result in the function returning a NaN and a warning. This function represents a function with some stocastic probability to sometimes fail. 
If we iterate this function a couple of times, store it in vector x and then try to get the sum it also results in a NaN.
Now lets try catch the error before it return a NaN and rerun the function. Change you do_calculation function to the following:
do_calculation<-function(){
  int<-sample(c(-1,1),1)
  tryCatch({
    sqrt(int)
  }, warning=function(w){
    do_calculation()
  })
}
We have replaced sqrt(int) with a tryCatch statement. The first argument is the expression to evaluate and the warning parameter allows you to fun some code when we get a warning. In out case we just want to run the function again, in the hope of sampling 1 instead of -1. Now when we run the function a few times we should be able to see that it always returns 1.
You can also add error as another parameter to catch errors intead of warnings. 
Last modified 3yr ago