Capturing table rows from an HTML page
Mining Hypertext Markup Language (HTML) is often a feat of identifying and parsing only its structured segments. Not all text in an HTML file may be useful, so we find ourselves only focusing on a specific subset. For instance, HTML tables and lists provide a strong and commonly used structure to extract data whereas a paragraph in an article may be too unstructured and complicated to process.
In this recipe, we will find a table on a web page and gather all rows to be used in the program.
Getting ready
We will be extracting the values from an HTML table, so start by creating an input.html file containing a table as shown in the following figure:
The HTML behind this table is as follows:
$ cat input.html
<!DOCTYPE html>
<html>
<body>
<h1>Course Listing</h1>
<table>
<tr>
<th>Course</th>
<th>Time</th>
<th>Capacity</th>
</tr>
<tr>
<td>CS 1501</td>
<td>17:00</td>
<td>60</td>
</tr>
<tr>
<td>MATH 7600</td>
<td>14:00</td>
<td>25</td>
</tr>
<tr>
<td>PHIL 1000</td>
<td>9:30</td>
<td>120</td>
</tr>
</table>
</body>
</html>If not already installed, use Cabal to set up the HXT library and the split library, as shown in the following command lines:
$ cabal install hxt $ cabal install split
How to do it...
- We will need the
htxpackage for XML manipulations and thechunksOffunction from the split package, as presented in the following code snippet:import Text.XML.HXT.Core import Data.List.Split (chunksOf)
- Define and implement
mainto read theinput.htmlfile.main :: IO () main = do input <- readFile "input.html"
- Feed the HTML data into
readString, thereby settingwithParseHTMLtoyesand optionally turning off warnings. Extract all thetdtags and obtain the remaining text, as shown in the following code:texts <- runX $ readString [withParseHTML yes, withWarnings no] input //> hasName "td" //> getText - The data is now usable as a list of strings. It can be converted into a list of lists similar to how CSV was presented in the previous CSV recipe, as shown in the following code:
let rows = chunksOf 3 texts print $ findBiggest rows
- By folding through the data, identify the course with the largest capacity using the following code snippet:
findBiggest :: [[String]] -> [String] findBiggest [] = [] findBiggest items = foldl1 (\a x -> if capacity x > capacity a then x else a) items capacity [a,b,c] = toInt c capacity _ = -1 toInt :: String -> Int toInt = read - Running the code will display the class with the largest capacity as follows:
$ runhaskell Main.hs {"PHIL 1000", "9:30", "120"}
How it works...
This is very similar to XML parsing, except we adjust the options of readString to [withParseHTML yes, withWarnings no].
