Replacing missing value when web scraping (rvest) - r

Question

I'm trying to write a script that will go through a list of players provided by the website Transfermarkt and gathering some information about them. For that, I've created the script below, but faced a problem with 1 of the 29 players in the list. Due to one page being arranged differently than the others, the code outputs a list of only 28 players since it can't find information on the aforementioned page.
I understand why the code I've written doesn't find any information on the given page and thus giving me a list of 28, but I don't know how to rewrite a code in order to achieve what I want:
for the script to simply replace the entry with a "-" if it does not find anything, in this case a nationality, for the node on a particular page and return a full list with 29 players with all the other info in it.
The player page in question is this and while the other pages has the node used in the code for nationality, here it's ".dataValue span".
I'm still quite new to R and it might be an easy fix, but atm I can't figure it out. Any help or advise is appreciated.
URL <- "http://www.transfermarkt.de/fc-bayern-munchen/leistungsdaten/verein/27/reldata/%262016/plus/1"
WS <- read_html(URL)
Team <- WS %>% html_nodes(".spielprofil_tooltip") %>% html_attr("href") %>% as.character()
Team <- paste0("http://www.transfermarkt.de",Team)
Catcher <- data.frame(Name=character(),Nat=character(),Vertrag=character())
for (i in Team) {
WS1 <- read_html(i)
Name <- WS1 %>% html_nodes("h1") %>% html_text() %>% as.character()
Nat <- WS1 %>% html_nodes(".hide-for-small+ p .dataValue span") %>% html_text() %>% as.character()
Vertrag <- WS1 %>% html_nodes(".dataValue:nth-child(9)") %>% html_text() %>% as.character()
if (length(Nat) > 0) {
temp <- data.frame(Name,Nat,Vertrag)
Catcher <- rbind(Catcher,temp)
}
else {}
cat("*")
}
num_Rows <- nrow(Catcher)
odd_indexes <- seq(1,num_Rows,2)
Catcher <- data.frame(Catcher[odd_indexes,])

Answer 1

It's honestly easier to scrape the whole table, just in case things move around. I find purrr is a helpful complement for rvest, allowing you to iterate over URLs and node lists and easily coerce results to data.frames:
library(rvest)
library(purrr)
# build dynamically if you like
urls <- c(boateng = 'http://www.transfermarkt.de/jerome-boateng/profil/spieler/26485',
friedl = 'http://www.transfermarkt.de/marco-friedl/profil/spieler/156990')
# scrape once, parse iteratively
html <- urls %>% map(read_html)
df <- html %>%
map(html_nodes, '.dataDaten p') %>%
map_df(map_df,
~list(
variable = .x %>% html_node('.dataItem') %>% html_text(trim = TRUE),
value = .x %>% html_node('.dataValue') %>% html_text(trim = TRUE) %>% gsub('\\s+', ' ', .)
),
.id = 'player')
df
#> # A tibble: 17 × 3
#> player variable value
#> <chr> <chr> <chr>
#> 1 boateng Geb./Alter: 03.09.1988 (28)
#> 2 boateng Geburtsort: Berlin
#> 3 boateng Nationalität: Deutschland
#> 4 boateng Größe: 1,92 m
#> 5 boateng Position: Innenverteidiger
#> 6 boateng Vertrag bis: 30.06.2021
#> 7 boateng Berater: SAM SPORTS
#> 8 boateng Nationalspieler: Deutschland
#> 9 boateng Länderspiele/Tore: 67/1
#> 10 friedl Geb./Alter: 16.03.1998 (19)
#> 11 friedl Nationalität: Österreich
#> 12 friedl Größe: 1,87 m
#> 13 friedl Position: Linker Verteidiger
#> 14 friedl Vertrag bis: 30.06.2021
#> 15 friedl Berater: acta7
#> 16 friedl Akt. Nationalspieler: Österreich U19
#> 17 friedl Länderspiele/Tore: 6/0
Alternately, that particular piece of data is in three places on those pages, so if one is inconsistent there's a chance the others are better. Or grab them from the table with the whole team—countries are not printed, but they're in the title attribute of the flag images, which can be grabbed with html_attr:
html <- read_html('http://www.transfermarkt.de/fc-bayern-munchen/leistungsdaten/verein/27/reldata/%262016/plus/1')
team <- html %>%
html_nodes('tr.odd, tr.even') %>%
map_df(~list(player = .x %>% html_node('a.spielprofil_tooltip') %>% html_text(),
nationality = .x %>% html_nodes('img.flaggenrahmen') %>% html_attr('title') %>% toString()))
team
#> # A tibble: 29 × 2
#> player nationality
#> <chr> <chr>
#> 1 Manuel Neuer Deutschland
#> 2 Sven Ulreich Deutschland
#> 3 Tom Starke Deutschland
#> 4 Jérôme Boateng Deutschland
#> 5 David Alaba Österreich
#> 6 Mats Hummels Deutschland
#> 7 Javi Martínez Spanien
#> 8 Juan Bernat Spanien
#> 9 Philipp Lahm Deutschland
#> 10 Rafinha Brasilien, Deutschland
#> # ... with 19 more rows