How to change value if error occurs in for loop? - r

Question

I have a loop that reads HTML table data from ~ 440 web pages. The code on each page is not exactly the same, so sometimes I need table node 1 and sometime I need node 2. Right now I've just been setting the node number manually in a list and feeding it into the loop. My problem is that the page nodes have started changing and updating the node # list is getting to be a hassle.
If the loop encounters the wrong node # (ie: 1 instead of 2, or reverse) it gives an error and shuts down. Is there a way to have the loop replace the erroneous node number to the correct one if it encounters an error, and then keep running the loop as if nothing happened?
Here's the readHTML portion of the code in my loop with an example url:
url <- "http://espn.go.com/nba/player/gamelog/_/id/2991280/year/2013/"
html.page <- htmlParse(url)
tableNodes <- getNodeSet(html.page, "//table")
x <- as.numeric(Players$Nodes[s])
tbl = readHTMLTable(tableNodes[[x]], colClasses = c("character"),stringsAsFactors = FALSE)
Here's the error I get when the node # is wrong:
"Error in readHTMLTable(tableNodes[[x]], colClasses = c("character"), stringsAsFactors = FALSE) : error in evaluating the argument 'doc' in selecting a method for function 'readHTMLTable': Error in tableNodes[[x]] : subscript out of bounds"
Example code:
A <- c("dog", "cat")
Nodes <- as.data.frame(1:1)
#)Nodes <- as.data.frame(1:2) <-- This works without errors
colnames(Nodes)[1] <- "Col1"
Nodes2 <- 2
url <-c("http://espn.go.com/nba/player/gamelog/_/id/6639/year/2013/","http://espn.go.com/nba/player/gamelog/_/id/6630/year/2013/")
for (i in 1:length(A))
{
html.page <- htmlParse(url[i])
tableNodes <- getNodeSet(html.page, "//table")
x <- as.numeric(Nodes$Col1[i])
df = readHTMLTable(tableNodes[[x]], colClasses = c("character"),stringsAsFactors = FALSE)
#tryCatch(df) here.....no clue
assign(paste0("", A[i]), df)
}

Answer 1

If you get subscript out of bounds error msg, then you should try to with a lower x for sure. General demo with tryCatch based on the demo code you posted in the original question (although I have replaced x with 2 as I have no idea what is Players and s):
> msg <- tryCatch(readHTMLTable(tableNodes[[2]], colClasses = c("character"),stringsAsFactors = FALSE), error = function(e)e)
> str(msg)
List of 2
$ message: chr "error in evaluating the argument 'doc' in selecting a method for function 'readHTMLTable': Error in tableNodes[[2]] : subscript"| __truncated__
$ call : language readHTMLTable(tableNodes[[2]], colClasses = c("character"), stringsAsFactors = FALSE)
- attr(*, "class")= chr [1:3] "simpleError" "error" "condition"
> msg$message
[1] "error in evaluating the argument 'doc' in selecting a method for function 'readHTMLTable': Error in tableNodes[[2]] : subscript out of bounds\n"
> grepl('subscript out of bounds', msg$message)
[1] TRUE