如何使用rvest爬取SVG中的<a>标签？R语言技术求助

Hey, let's break down how to grab those SVG links you're after—your current code only pulls header links because it's not targeting the SVG-specific elements correctly. Here's what you can do:

First, Check the SVG's Structure #

Start by right-clicking the map in your browser and inspecting it to figure out how it's loaded:

• If it's an <svg> tag directly nested in the HTML (the most common setup for interactive maps), we can target it directly.
• If it's loaded via <object>/<embed> or an <img> (note: <img> won't let you scrape internal links), you'll need to first grab the SVG's source URL.

Step 1: Target SVG Links with rvest (Static Content) #

If the SVG is embedded in the HTML, adjust your selector to specifically look for links inside the SVG. SVG links might use standard <a> tags, but older SVGs often use xlink:href instead of the regular href attribute. Try this:

library(rvest)

# First, handle login with a persistent session (if required)
session <- session("https://your-target-login-page.com")
# Fill out the login form (replace with your form's actual field names)
login_form <- html_form(session)[[1]]
filled_form <- set_values(login_form, 
                          username = "your-username", 
                          password = "your-password")
session <- session_submit(session, filled_form)

# Navigate to the page with the SVG map
map_page <- session %>% session_jump_to("https://your-map-page.com")

# Grab <a> tags nested inside the SVG
svg_a_tags <- map_page %>% html_nodes("svg a")

# Extract links—check both href and xlink:href (SVG-specific attribute)
svg_links <- svg_a_tags %>% 
  html_attr("href") %>% 
  # Fall back to xlink:href if href is missing
  ifelse(is.na(.), html_attr(svg_a_tags, "xlink:href"), .)

# Convert relative URLs to absolute ones (critical for usable links)
base_url <- "https://your-target-domain.com"
absolute_links <- url_absolute(svg_links, base_url)

Step 2: Handle Dynamic SVG Content (JS-Rendered) #

If the SVG loads after the initial page load (via JavaScript), rvest won't see it because it only parses static HTML. For this, use a browser automation tool like RSelenium to render the page fully:

Example with RSelenium: #

library(RSelenium)
library(rvest)

# Start a Chrome driver (ensure ChromeDriver is installed and in your system PATH)
driver <- rsDriver(browser = "chrome", port = 4567L)
remDr <- driver[["client"]]

# Navigate to login page and authenticate
remDr$navigate("https://your-target-login-page.com")
remDr$findElement(using = "id", value = "username-input")$sendKeysToElement(list("your-username"))
remDr$findElement(using = "id", value = "password-input")$sendKeysToElement(list("your-password"))
remDr$findElement(using = "css selector", value = "button[type='submit']")$clickElement()

# Wait for login to complete, then go to the map page
Sys.sleep(2) # Adjust wait time based on your page's load speed
remDr$navigate("https://your-map-page.com")

# Get the fully rendered page source
page_source <- remDr$getPageSource()[[1]]
map_page <- read_html(page_source)

# Extract SVG links like before
svg_links <- map_page %>% 
  html_nodes("svg a") %>% 
  html_attr("href") %>% 
  ifelse(is.na(.), html_attr(., "xlink:href"), .)

# Clean up the browser session
remDr$close()
driver$server$stop()

Quick Tips #

• Always use your browser's dev tools to confirm what attribute holds the links (it could be href, xlink:href, or even a custom data attribute like data-link).
• If the SVG is a separate file (e.g., <object data="/maps/usa.svg">), grab that data URL, use your authenticated session to fetch it, then parse it as XML to extract links.

内容的提问来源于stack exchange，提问作者rotz