try                   package:base                   R Documentation

Try an Expression Allowing Error Recovery

Description:

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

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'.

Value:

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

See Also:

     'options' for setting error handlers and suppressing the printing
     of error messages; 'geterrmessage' for retrieving the last error
     message. 'tryCatch' provides another means of catching and
     handling errors.

Examples:

     ## 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"))])

