Advanced data collection: In-depth discussion of PHP and regular expression processing techniques

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:

1. Ordinary characters: Match the specified character itself.
   Example: pattern: "abc" string: "abcdefg" Matching result: "abc"

2. 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"
   

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3. Character class: matches any character within square brackets.
   Example: pattern: "[abc]" string: "abcdefg" Matching results: "a","b","c"

4. 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"
   

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5. Capture group: Store the matched substring in a variable for subsequent use.
   Example: pattern: "(w )@(w ).com" string: "tom@qq.com" Matching result: "tom","qq"

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.

1. Get links:
   Getting all links in a web page is a common requirement. We can use regular expressions to match the tags in HTML and then extract the link address.
   Sample code:

$pattern = '/]*?href=["']([^"'s]+)/i';
$html = file_get_contents("http://www.example.com");
preg_match_all($pattern, $html, $matches);
$links = $matches[1];
print_r($links);

2. Extract images:
   When grabbing images, we can use regular expressions to match all tags in HTML, and then extract The map's address.
   Sample code:

$pattern = '/]*?src=["']([^"'s]+)/i';
$html = file_get_contents("http://www.example.com");
preg_match_all($pattern, $html, $matches);
$images = $matches[1];
print_r($images);

3. Matching tables:
   Regular expressions can also be used to match and extract tables in HTML. The sample code below shows how to match and extract data from a two-dimensional table.

$pattern = '/(.*?)/s';
$html = file_get_contents("http://www.example.com");
preg_match($pattern, $html, $table);
$table_rows = $table[1];

$row_pattern = '/(.*?)/s';
preg_match_all($row_pattern, $table_rows, $rows);
$table_data = array();

foreach ($rows[1] as $row) {
    $column_pattern = '/(.*?)/s';
    preg_match_all($column_pattern, $row, $columns);
    $table_data[] = $columns[1];
}

print_r($table_data);

3. Summary