R language Crawler: CSS methods vs. XPath methods (Code implementation)

Both the CSS selector and the XPath method are used to locate the tags of the DOM tree, but there are some differences in the positioning representation of the two:

• CSS Method Extraction Node

library("rvest")single_table_page <- read_html("single-table.html")# 提取url里的所有表格html_table(single_table_page)html_table(html_node(single_table_page,"table"))products_page <- read_html("./case/products.html")products_page %>% html_nodes(".product-list li .name") %>% html_text() product_items <- products_page %>% html_nodes(".product-list li")data.frame(name = product_items %>% html_nodes(".name") %>% html_text(),            price = product_items %>% html_nodes(".price") %>%html_text()            %>% str_replace_all(pattern="\\$",replacement="") %>%                as.numeric(), stringsAsFactors = FALSE)

• XPath Method Extraction Node

page <- read_html("./case/new-products.html")#查找所有p节点page %>% html_nodes(xpath="//p")#CSS's waypage %>% html_nodes("p")# 找到所有具有class属性的li标签# xpath's waypage %>% html_nodes(xpath="//li[@class]")# CSS's waypage %>% html_nodes("li[class]")# 找到id=‘list’的div标签下的所有li标签# xparth's waypage %>% html_nodes(xpath="//div[@id='list']/ul/li")# CSS's waypage %>% html_nodes("div#list > ul > li")# 查找包含p节点的所有div节点page %>% html_nodes(xpath="//div[p]")# 查找所有class值为“info-value”，文本内容为“Good”的span节点page %>% html_nodes(xpath = "//span[@class='info-value' and text()='Good']")

R language Crawler: CSS methods vs. XPath methods (Code implementation)