Read list items with {rvest} using CSS or XPath selectors

rvest_ReadListItems.R

# Load library
library(rvest)

# -----------------------
# Read the web page
# -----------------------
link <- "http://www.adirondacklakessurvey.org/alscrpt.inc.php?alscpond=020225B&pname=ALLEGANY%20BROOK%20POND"
# NOTE: is ethical to store the page and not read it unnecessarily too many times, 
# overloading their server
link.scrap <- read_html(link)

# -----------------------
# Read all list items from the page
# -----------------------
all.list.items <- html_nodes(x   = link.scrap, 
                             css = "li") %>% 
                  html_text()
all.list.items[1:5]
## [1] "Location/General"
## [2] "Pond Name: ALLEGANY BROOK POND"
## [3] "Pond #: 020225B"                
## [4] "Town: Black Brook"             
## [5] "County: Clinton" 

# -----------------------
# Read a particular list item - use its CSS selector
# -----------------------
pond.name <- html_nodes(x   = link.scrap, 
                        css = "#historic_report_location > ul > ul > li:nth-child(1)") %>% 
             html_text()
pond.name
## [1] "Pond Name: ALLEGANY BROOK POND"

# This is the same as:
all.list.items[2]
## [1] "Pond Name: ALLEGANY BROOK POND"

# -----------------------
# Or, read a particular list item by using its XPath selector
# -----------------------
pond.name <- html_nodes(x     = link.scrap, 
                        xpath = '//*[@id="historic_report_location"]/ul/ul/li[1]') %>% 
             html_text()
pond.name
## [1] "Pond Name: ALLEGANY BROOK POND"

# -----------------------
# The non-piping (without the %>%) goes like:
# -----------------------
pond.name.node <- html_nodes(x     = link.scrap, 
                             xpath = '//*[@id="historic_report_location"]/ul/ul/li[1]')
pond.name.node
## {xml_nodeset (1)}
## [1] <li style="list-style-type:none">Pond Name: ALLEGANY BROOK POND</li>
pond.name <- html_text(pond.name.node)
pond.name
## [1] "Pond Name: ALLEGANY BROOK POND"