# 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:

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:

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.

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