Same webscrape code works on one page, not another using rvest - r

Question

I built a simple scrape to get a data frame with NFL draft results for 2020. I intent to use this code to map several years of results but for some reason, when I change the code for a single page scrape for any other year than 2020, I get the error at the bottom.
library(tidyverse)
library(rvest)
library(httr)
library(curl)
This scrape for 2020 works flawlesslessy, although the col names are in row 1 which isn't a big deal to me as I can deal with this later (mentioning though in case this might have to do with the problem):
x <- "https://www.pro-football-reference.com/years/2020/draft.htm"
df <- read_html(curl(x, handle = curl::new_handle("useragent" = "Mozilla/5.0"))) %>%
html_nodes("table") %>%
html_table() %>%
as.data.frame()
below the url is changed from 2020 to 2019 which is an active page with a table of the same format. For some reason, the same call as above does not work:
x <- "https://www.pro-football-reference.com/years/2019/draft.htm"
df <- read_html(curl(x, handle = curl::new_handle("useragent" = "Mozilla/5.0"))) %>%
html_nodes("table") %>%
html_table() %>%
as.data.frame()
Error in (function (..., row.names = NULL, check.rows = FALSE, check.names = TRUE, :
arguments imply differing number of rows: 261, 2

Answer 1

There are two tables at the url provided. There is the core draft (table 1, id = "drafts") and the supplemental draft (table 2, id = "drafts_supp").
The as.data.frame() call fails because it is trying to combine the two tables but they have differing columns in both name and number. You can direct rvest to read just the specific table you are interested in by providing the html_node() with either the xpath or the selector. You can find the xpath or selector by inspecting the specific table you are interested in, right-click > inspect on Chrome/Mozilla. Note that for selector to use id you'll need to use #drafts not just drafts and for xpath you typically have to wrap the text in single quotes.
This works: html_node(xpath = '//*[#id="drafts"]')
This doesn't because of the double quotes: html_node(xpath = "//*[#id="drafts"]")
Note that I believe the html_nodes("table") used in your example is unnecessary, as html_table() already selects only tables.
x <- "https://www.pro-football-reference.com/years/2019/draft.htm"
raw_html <- read_html(x)
# use xpath
raw_html %>%
html_node(xpath = '//*[#id="drafts"]') %>%
html_table()
# use selector
raw_html %>%
html_node("#drafts") %>%
html_table()