从指定XML链接提取表格遇阻，求R语言优化方案

Hey there! Let's break down your problem and find better solutions for extracting that table data, plus clarify the differences between rvest's html_* and xml_* functions.

1. Why your initial rvest attempts failed #

The URL you're targeting returns an XML document, not HTML. When you use read_html(), it parses the XML as if it were HTML, which misinterprets the structure—hence why html_nodes("table") and .report td didn't work as expected.

2. Key differences between html_* and xml_* functions #

• html_* functions: Built for HTML documents. They leverage CSS selectors (like .report td) and have helper functions like html_table() tailored to standard HTML table structures (with <thead>, <tr>, <td> tags following web conventions).
• xml_* functions: Designed for XML documents, which have more flexible (and sometimes unstructured) tag names. XML doesn't have a universal "table" standard like HTML, so there's no xml_table() function. Instead, you use XPath queries to target specific nodes and extract their content manually.

3. A simpler XML-based solution (no RSelenium needed) #

Since the source is XML, use the xml2 package (which rvest relies on under the hood) to parse it directly into a dataframe. Here's how:

library(xml2)

url <- "http://reports.ieso.ca/public/GenOutputbyFuelHourly/PUB_GenOutputbyFuelHourly.xml"
xml_doc <- read_xml(url)

# Extract all table rows
rows <- xml_find_all(xml_doc, "//table/tr")

# Get header text from the first row's <th> tags
header <- xml_text(xml_find_all(rows[1], "./th"))

# Extract data from remaining rows' <td> tags
table_data <- lapply(rows[-1], function(row) {
  xml_text(xml_find_all(row, "./td"))
})

# Convert to a dataframe and set column names
df <- as.data.frame(do.call(rbind, table_data), stringsAsFactors = FALSE)
colnames(df) <- header

4. Optimizing your RSelenium workflow #

If you still prefer using RSelenium (maybe for more dynamic content), you can skip manually splitting the values vector by grabbing the table's HTML directly and parsing it with rvest:

library(RSelenium)
library(rvest)

remDr <- remoteDriver(port = 4567L, browserName = "phantomjs")
remDr$open()
remDr$navigate(url)

# Grab the full HTML of the table element
table_html <- remDr$findElement("css", ".report table")$getElementAttribute("outerHTML")[[1]]

# Parse the HTML table directly into a dataframe
df <- read_html(table_html) %>% html_table() %>% .[[1]]

remDr$close()

This way, you avoid the tedious step of splitting the vector into rows—rvest handles the table structure for you once you have the HTML.

内容的提问来源于stack exchange，提问作者jsg51483