# try

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##### Try an Expression Allowing Error Recovery

try is a wrapper to run an expression that might fail and allow the user's code to handle error-recovery.

Keywords
programming
##### Usage
try(expr, silent = FALSE)
##### Arguments
expr
an R expression to try.
silent
logical: should the report of error messages be suppressed?
##### Details

try evaluates an expression and traps any errors that occur during the evaluation. If an error occurs then the error message is printed to the stderr connection unless options("show.error.messages") is false or the call includes silent = TRUE. The error message is also stored in a buffer where it can be retrieved by geterrmessage. (This should not be needed as the value returned in case of an error contains the error message.)

try is implemented using tryCatch; for programming, instead of try(expr, silent = TRUE), something like tryCatch(expr, error = function(e) e) (or other simple error handler functions) may be more efficient and flexible.

##### Value

The value of the expression if expr is evaluated without error, but an invisible object of class "try-error" containing the error message, and the error condition as the "condition" attribute, if it fails.

options for setting error handlers and suppressing the printing of error messages; geterrmessage for retrieving the last error message. The underlying tryCatch provides more flexible means of catching and handling errors.

assertCondition in package tools is related and useful for testing.

• try
##### Examples
library(base) ## this example will not work correctly in example(try), but ## it does work correctly if pasted in options(show.error.messages = FALSE) try(log("a")) print(.Last.value) options(show.error.messages = TRUE) ## alternatively, print(try(log("a"), TRUE)) ## run a simulation, keep only the results that worked. set.seed(123) x <- stats::rnorm(50) doit <- function(x) { x <- sample(x, replace = TRUE) if(length(unique(x)) > 30) mean(x) else stop("too few unique points") } ## alternative 1 res <- lapply(1:100, function(i) try(doit(x), TRUE)) ## alternative 2 ## Not run: res <- vector("list", 100) # for(i in 1:100) res[[i]] <- try(doit(x), TRUE)## End(Not run) unlist(res[sapply(res, function(x) !inherits(x, "try-error"))]) 
Documentation reproduced from package base, version 3.1.3, License: Part of R 3.1.3

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