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Advanced data collection: In-depth discussion of PHP and regular expression processing techniques
Introduction:
Data collection is one of the key steps in modern data analysis and mining. On the Internet, we can use various technologies to crawl the required data from web pages. As a popular server-side scripting language, PHP has powerful data processing capabilities. Combined with regular expressions, we can process and extract data more flexibly and efficiently. This article will delve into PHP and regular expression processing techniques, and provide some practical code examples.
1. Regular expression basics
Regular expression is a powerful tool used to match, find and replace strings. In PHP, we can use preg_match(), preg_match_all(), preg_replace() and other functions to operate regular expressions. The following are some commonly used regular expression patterns and their meanings:
Metacharacters: characters with special meaning.
Example: pattern: "." string: "a.bc.defg" Matching results: "a","b","c","d","e","f","g"
pattern: "d" string: "12345" 匹配结果: "1","2","3","4","5"
Repeat qualifier: determine the number of matching characters.
Example: pattern: "a " string: "aaabbbccc" Matching result: "aaa"
pattern: "d{2,4}" string: "12345" 匹配结果: "1234"
2. Data collection Tips
In data collection, we usually need to obtain specific information in web pages, such as titles, links, pictures, etc. Below are several common data collection techniques, with corresponding PHP code examples.
$pattern = '/<as+[^>]*?href=["']([^"'s]+)/i'; $html = file_get_contents("http://www.example.com"); preg_match_all($pattern, $html, $matches); $links = $matches[1]; print_r($links);
$pattern = '/<imgs+[^>]*?src=["']([^"'s]+)/i'; $html = file_get_contents("http://www.example.com"); preg_match_all($pattern, $html, $matches); $images = $matches[1]; print_r($images);
$pattern = '/<table>(.*?)</table>/s'; $html = file_get_contents("http://www.example.com"); preg_match($pattern, $html, $table); $table_rows = $table[1]; $row_pattern = '/<tr>(.*?)</tr>/s'; preg_match_all($row_pattern, $table_rows, $rows); $table_data = array(); foreach ($rows[1] as $row) { $column_pattern = '/<td>(.*?)</td>/s'; preg_match_all($column_pattern, $row, $columns); $table_data[] = $columns[1]; } print_r($table_data);
3. Summary
This article deeply discusses the processing skills of PHP and regular expressions, and their application in data collection is particularly important. By understanding the basics and common patterns of regular expressions, we can extract the data we need more flexibly and efficiently. In addition, the article also provides multiple practical code examples for readers to refer to and learn from. I hope this article will be helpful to readers in their study and practice in the field of data collection!
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