# 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:

```r
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.&#x20;

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:

```r
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.&#x20;