R How to make a for loop without knowing the length?

Question

Currently on this site I am scraping in the shot chart information. To scrape in the info I need to make a for loop for however many shots there are. I find the number of shots by clicking "Team Stats" and finding the number of field goal attempts.

I would like to make the proper for loop without having to find out the number of shots.

What I am currently doing:

shotchart <- data.frame(shot=as.vector(0), class=as.vector(0), data_homeaway=as.vector(0), 
                    data_period=as.vector(0), player_id=as.vector(0), data_text=as.vector(0),
                    location=as.vector(0), gamenumber= as.vector(0))

for (i in 1:54)
{
 text <-paste0("//*[(@class='shots home-team')]//*[(@id)][",i,"]")
 shotchart[nrow(shotchart)+1,1]<- unlist(re$findElement(using='xpath',text)$getElementAttribute('id'))
shotchart[nrow(shotchart),2]<- unlist(re$findElement(using='xpath', text)$getElementAttribute('class'))
shotchart[nrow(shotchart),3]<-unlist(re$findElement(using='xpath', text)$getElementAttribute('data-homeaway'))
shotchart[nrow(shotchart),4]<-unlist(re$findElement(using='xpath', text)$getElementAttribute('data-period'))
shotchart[nrow(shotchart),5]<-unlist(re$findElement(using='xpath', text)$getElementAttribute('data-shooter'))
shotchart[nrow(shotchart),6]<-unlist(re$findElement(using='xpath', text)$getElementAttribute('data-text'))
shotchart[nrow(shotchart),7]<-unlist(re$findElement(using='xpath', text)$getElementAttribute('style'))
shotchart[nrow(shotchart),8]<-k-1

}

Any help will be appreciated. Please let me know if any further information is needed.

Answer 1

library(RSelenium)
checkForServer()
startServer()
Sys.sleep(5)
re<-remoteDriver()
re$open()
re$navigate("http://espn.go.com/mens-college-basketball/playbyplay?gameId=400830392")

shotchart <- data.frame(shot=as.vector(0), class=as.vector(0), data_homeaway=as.vector(0), 
                        data_period=as.vector(0), player_id=as.vector(0), data_text=as.vector(0),
                        location=as.vector(0), gamenumber= as.vector(0))
error="Error : \t Summary: NoSuchElement\n \t Detail: An element could not be located on the page using the given search parameters.\n \t class: org.openqa.selenium.NoSuchElementException\n"
i<-1
element=0
while ((i>0)&(element[1]!=error))
{
  text <-paste0("//*[(@class='shots home-team')]//*[(@id)][",i,"]")
  element<- try(unlist(re$findElement(using='xpath', text)$getElementAttribute('id')),silent = TRUE)
  if (element[1]==error)
    break;
  shotchart[nrow(shotchart)+1,1]<- unlist(re$findElement(using='xpath',text)$getElementAttribute('id'))
  shotchart[nrow(shotchart),2]<- unlist(re$findElement(using='xpath', text)$getElementAttribute('class'))
  shotchart[nrow(shotchart),3]<-unlist(re$findElement(using='xpath', text)$getElementAttribute('data-homeaway'))
  shotchart[nrow(shotchart),4]<-unlist(re$findElement(using='xpath', text)$getElementAttribute('data-period'))
  shotchart[nrow(shotchart),5]<-unlist(re$findElement(using='xpath', text)$getElementAttribute('data-shooter'))
  shotchart[nrow(shotchart),6]<-unlist(re$findElement(using='xpath', text)$getElementAttribute('data-text'))
  shotchart[nrow(shotchart),7]<-unlist(re$findElement(using='xpath', text)$getElementAttribute('style'))
  shotchart[nrow(shotchart),8]<-i-1
  i<-i+1
}

I am not sure as what your variable k means.

I took advice from all the comments.