For loop skip if table does not exist - r

Question

Ran in to another problem. I have a for loop that contains urls to scrape batting information from a table with the id batting_gamelogs. If that id does not exist on the page then move on to the next url else scrape the table.
I think it should be something like this below, but I can't get it to work.
if xpathSApply(batting, '//*[#id != "batting_gamelogs"]')[[1]] next
else
{
tableNode <- xpathSApply(batting, '//*[#id="batting_gamelogs"]')[[1]]
data <- readHTMLTable(tableNode, stringsAsFactors = FALSE)
data # select the first table
total <- cbind(id,year,data)
batlist <- rbind(batlist, total)
}
I have attached sample code.
#SCRAPE BATTING STATS
data = NULL
batlist = NULL
battingURLs <- paste("http://www.baseball-reference.com",yplist[,c("hrefs")],sep="")
for(thisbattingURL in battingURLs){
batting <- htmlParse(thisbattingURL)
fstampid <- regexpr("&", thisbattingURL, fixed=TRUE)-1
fstampyr <- regexpr("year=", thisbattingURL, fixed=TRUE)+5
id <- substr(thisbattingURL, 53, fstampid)
year <- substr(thisbattingURL, fstampyr, 75)
tableNode <- xpathSApply(batting, '//*[#id="batting_gamelogs"]')[[1]]
data <- readHTMLTable(tableNode, stringsAsFactors = FALSE)
data # select the first table
total <- cbind(id,year,data)
batlist <- rbind(batlist, total)
}
batlist
Any help is much appreciated!

Answer 1

I can't get it to work.
This phrase should always be a reminder to tell what actually happened (and how it differs from what you expected to happen). I suspect what happened was that it skipped too often (vs. not skipping when it should have). But you could tell us that, instead of leaving us to figure it out.
if xpathSApply(batting, '//*[#id != "batting_gamelogs"]')[[1]] next
The "not" is in the wrong place. Here, you're saying, skip this iteration if there is an element on the page that has an id attribute whose value is not batting_gamelogs. Instead you want to skip this iteration if there is no element on the page that has an id attribute whose value is batting_gamelogs.
So, use this for your XPath expression:
'//*[#id = "batting_gamelogs"]'
and put the "not" outside of xpathSApply(), by testing whether the length of the result list is zero (thanks to the answer at https://stackoverflow.com/a/25553805/423105):
if (length(xpathSApply(batting, '//*[#id = "batting_gamelogs"]')) == 0) next
I took out the [[1]] because you just want to test whether any values are returned; you don't care about extracting the first result.