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copied!<p>The only really detailed explanation I have seen can be found here: <a href="http://mazamascience.com/WorkingWithData/?p=912" rel="nofollow">http://mazamascience.com/WorkingWithData/?p=912</a></p> <p>Here is a code clip from that blog post showing how tryCatch works</p> <pre><code>#!/usr/bin/env Rscript # tryCatch.r -- experiments with tryCatch # Get any arguments arguments <- commandArgs(trailingOnly=TRUE) a <- arguments[1] # Define a division function that can issue warnings and errors myDivide <- function(d, a) { if (a == 'warning') { return_value <- 'myDivide warning result' warning("myDivide warning message") } else if (a == 'error') { return_value <- 'myDivide error result' stop("myDivide error message") } else { return_value = d / as.numeric(a) } return(return_value) } # Evalute the desired series of expressions inside of tryCatch result <- tryCatch({ b <- 2 c <- b^2 d <- c+2 if (a == 'suppress-warnings') { e <- suppressWarnings(myDivide(d,a)) } else { e <- myDivide(d,a) # 6/a } f <- e + 100 }, warning = function(war) { # warning handler picks up where error was generated print(paste("MY_WARNING: ",war)) b <- "changing 'b' inside the warning handler has no effect" e <- myDivide(d,0.1) # =60 f <- e + 100 return(f) }, error = function(err) { # warning handler picks up where error was generated print(paste("MY_ERROR: ",err)) b <- "changing 'b' inside the error handler has no effect" e <- myDivide(d,0.01) # =600 f <- e + 100 return(f) }, finally = { print(paste("a =",a)) print(paste("b =",b)) print(paste("c =",c)) print(paste("d =",d)) # NOTE: Finally is evaluated in the context of of the inital # NOTE: tryCatch block and 'e' will not exist if a warning # NOTE: or error occurred. #print(paste("e =",e)) }) # END tryCatch print(paste("result =",result)) </code></pre>

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