-
-
Save javieroot/e2b02ea44e7d2670453f461b245d08e6 to your computer and use it in GitHub Desktop.
tryCatch in R
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
urls <- c( | |
"http://stat.ethz.ch/R-manual/R-devel/library/base/html/connections.html", | |
"http://en.wikipedia.org/wiki/Xz", | |
"xxxxx" | |
) | |
readUrl <- function(url) { | |
out <- tryCatch( | |
{ | |
# Just to highlight: if you want to use more than one | |
# R expression in the "try" part then you'll have to | |
# use curly brackets. | |
# 'tryCatch()' will return the last evaluated expression | |
# in case the "try" part was completed successfully | |
message("This is the 'try' part") | |
readLines(con=url, warn=FALSE) | |
# The return value of `readLines()` is the actual value | |
# that will be returned in case there is no condition | |
# (e.g. warning or error). | |
# You don't need to state the return value via `return()` as code | |
# in the "try" part is not wrapped insided a function (unlike that | |
# for the condition handlers for warnings and error below) | |
}, | |
error=function(cond) { | |
message(paste("URL does not seem to exist:", url)) | |
message("Here's the original error message:") | |
message(cond) | |
# Choose a return value in case of error | |
return(NA) | |
}, | |
warning=function(cond) { | |
message(paste("URL caused a warning:", url)) | |
message("Here's the original warning message:") | |
message(cond) | |
# Choose a return value in case of warning | |
return(NULL) | |
}, | |
finally={ | |
# NOTE: | |
# Here goes everything that should be executed at the end, | |
# regardless of success or error. | |
# If you want more than one expression to be executed, then you | |
# need to wrap them in curly brackets ({...}); otherwise you could | |
# just have written 'finally=<expression>' | |
message(paste("Processed URL:", url)) | |
message("Some other message at the end") | |
} | |
) | |
return(out) | |
} |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment