Customizing the readHTMLTable Function to Handle Collapsing Span Elements

In this article, we’ll explore how to use the XML package in R to parse HTML tables, including those with collapsing span elements. We’ll define a custom function to handle the parsing of cells in the table and demonstrate how to use it to extract specific data.

Introduction

The readHTMLTable function from the XML package is useful for parsing HTML tables in R. However, when dealing with tables that contain collapsible span elements, this function can produce unexpected results. In this article, we’ll show how to define a custom function to parse cells in the table and handle these collapsing span elements.

Understanding Collapsing Span Elements

Collapsing span elements are HTML elements (in this case, <span>) that collapse together when rendered. This means that the browser will attempt to merge adjacent elements with the same class or other styles into a single element.

In the context of the readHTMLTable function, collapsing span elements can lead to unexpected results. For example, if the date column in the table contains collapsible span elements, extracting the data from this column using readHTMLTable might result in a collapsed string instead of individual dates.

Defining a Custom Function for Parsing Cells

To handle collapsing span elements, we need to define a custom function that can parse cells in the table. This function will check if there are any <span> elements with a specific class ("shsGameDate" or "shsTimezone"), and if so, extract the data from these elements.

myFun <- function(x) {
  # Check for date column span elements
  y <- getNodeSet(x, "./span[@class=\"shsGameDate\"]")
  if (length(y) > 0) {
    # Extract the date value from the first span element
    return(xmlValue(y[[1]]))
  }
  
  # Check for time zone column span elements
  y <- getNodeSet(x, "./span[@class=\"shsTimezone shsETZone\"]")
  if (length(y) > 0) {
    # Extract the time value from the first span element
    return(xmlValue(y[[1]]))
  }
  
  # If no specific classes are found, extract the raw HTML value
  xmlValue(x, encoding = "UTF-8")
}

Using the Custom Function with readHTMLTable

Now that we have defined our custom function myFun, we can use it with readHTMLTable to parse cells in the table.

library(XML)
url <- 'http://scores.nbcsports.msnbc.com/cbk/teamstats.asp?team=1115&report=schedule'
raw.schedule <- readHTMLTable(url, which = 2, elFun = myFun)

# Print the first few rows of the parsed schedule table
head(raw.schedule)

Example Output

Here’s an example output of using our custom function with readHTMLTable:

Conclusion

In this article, we demonstrated how to use the XML package in R to parse HTML tables with collapsing span elements. By defining a custom function to handle parsing cells in the table, we can extract specific data from these tables.

This technique is useful when working with web scraping or data extraction tasks where tables may contain collapsible elements. Remember to always check for different versions of your target website and adjust your code accordingly to maintain compatibility.

Additional Tips

• Always test your custom functions on a small sample before applying them to larger datasets.
• Be aware that some browsers or rendering engines might render the HTML differently, which could affect the output of your custom function.

Last modified on 2025-02-04