CODEWITHSUNDEEP
rlistdebuggingfor-loop
user1357015
user1357015

Reputation: 11686

how to figure out which statement in lapply fails in R

I often have the situation like this:

result <- lapply(1:length(mylist), function(x){
doSomething(x)
})

However, if it fails, I have no idea which element in the list failed on doSomething().

So then I end up recoding it as a for loop:

for(i in 1: length(mylist)){
doSomething(mylist[[i]])
}

I can then see the last value of i and what happened. There must be a better way to do this right?? Thanks!

Upvotes: 1

Views: 540

Answers (2)

Martin Morgan
Martin Morgan

Reputation: 46856

Notice how the error includes 5L

> lapply(1:10, function(i) if (i == 5) stop("oops"))
Error in FUN(1:10[[5L]], ...) : oops

indicating that the 5th iteration failed.

Upvotes: 3

Greg Snow
Greg Snow

Reputation: 49640

One simple option is to run the code:

options( error=recover )

before running lapply (see ?recover for details).

Then when/if an error occurs you will instantly be put into the recover mode that will let you examine which function you are in, what arguments were passed to that function, etc. so you can see which step you are on and what the possible reason for the error is.

You can also use try or tryCatch as mentioned in the comments to either skip elements that produce an error or print out information on where they occur.

Upvotes: 2

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