Manipulating two characters in url with purrr package for scraping pupose - r

Question

I'm having difficulties writing a scrape function with the purrr package (first time). I want to scrape multiple pages by changing two characters of the designated url. The following code works for only one season of football players data.
page_func <- function(page) {
cat(".")
df <- read_html(paste0("http://www.voetbal.com/spelerslijst/ned-eredivisie-2017-2018/nach-name/",
page)) %>%
html_nodes("table") %>%
html_table() %>%
as.data.frame() %>%
as.tbl() %>%
select(Speler, Team, Geboren, Lengte, Positie) %>%
add_column(seizoen = "2017-2018")
}
raw_seizoen_17_18 <- map_df(1:11, page_func)
Output:
# A tibble: 541 x 6
Speler Team Geboren Lengte Positie seizoen
<chr> <chr> <chr> <chr> <chr> <chr>
1 Amir Absalem FC Groningen 19.06.1997 ??? VD 2017-2018
2 Asumah Abubakar Willem II 10.05.1997 183 cm AV 2017-2018
3 Ragnar Ache Sparta Rotterdam 28.07.1998 182 cm AV 2017-2018
4 Marouane Afaker SBV Excelsior 09.05.1999 ??? AV 2017-2018
5 Gor Agbaljan Heracles Almelo 25.04.1997 183 cm MV 2017-2018
6 Thomas Agyepong NAC Breda 10.10.1995 168 cm AV 2017-2018
Now I want to scrape all seasons from 1956-1957 untill 2017-2018 in one function, but I can't yet figure out how to manipulate these two variables with purrr.
page_season_func <- function(seizoen, page) {
cat(".")
df <- read_html(paste0("http://www.voetbal.com/spelerslijst/ned-eredivisie-",
seizoen,
"/nach-name/",
page)) %>%
html_nodes("table") %>%
html_table() %>%
as.data.frame() %>%
as.tbl() %>%
select(Speler, Team, Geboren, Lengte, Positie) %>%
add_column(year = seizoen)
}

Answer 1

seasons <-
1956:2017 %>%
paste(., . + 1, sep = "-")
res <-
cross2(seasons, 1:11) %>%
transpose() %>%
pmap_df(page_season_func)

Answer 2

You can use map2_dfr, with the .id tag to specify the year in your output:
page_span <- 1:11
year_span <- 1956:1958
years <- sort(rep(year_span, length(page_span)))
names(years) <- years # need to name years for .id to work
pages <- rep(page_span, length(year_span))
map2_dfr(years, pages, page_season_func, .id="year")
Output:
# A tibble: 6 x 6
year Speler Team Geboren Lengte Positie
<chr> <chr> <chr> <chr> <chr> <chr>
1 1956 Sjeng Adang Roda JC Kerk… 04.07.19… ??? MV
2 1956 Wim Anderiesen jr. AFC Ajax 02.09.19… ??? VD
3 1956 Wim Andriesen AFC Ajax 09.02.19… ??? MV
4 1956 Aad Bak Feyenoord 18.06.19… ??? MV
5 1956 Huub Bisschops Roda JC Kerk… 22.01.19… ??? AV
6 1956 Wim Bleijenberg AFC Ajax 05.11.19… ??? AV
A couple of changes to page_season_func():
seizoen2 is created, which makes the y1-y2 format from y1 as input
no need to add a year column, now that you can use map2_dfr's .id argument
page_season_func <- function(seizoen, page) {
cat(".")
seizoen2 <- paste(seizoen, seizoen+1, sep="-")
df <- read_html(paste0("http://www.voetbal.com/spelerslijst/ned-eredivisie-",
seizoen2,
"/nach-name/",
page)) %>%
html_nodes("table") %>%
html_table(fill=TRUE) %>%
as.data.frame() %>%
as.tbl() %>%
select(Speler, Team, Geboren, Lengte, Positie)
}