PHP数组交集 - 查找公共子集

Question

I have data stored in mongodb collection - pages. Each page has following attributes:

    title - string 
    id - number
    contents - it is an object with 3 attribute
       contents.topic  - string
       contents.parentTopic - number
       contents.text - string

I have roughly 500 pages stored in DB and performance isn't a very big consideration for me.

I need to find common contents across all pages. If I do following:

    $pages = $db->selectCollection("pages");       
    $cursor = $pages->find(array());
    $data = array();

    foreach ( $cursor as $page ){
        array_push($data,$page);
    }
    $intersect = call_user_func_array('array_intersect_assoc',$data);
    echo "<pre>";
    print_r($intersect);

Like this I can get common contents across all pages which is working fine. This is true as long as there is at least one common 'content' across all pages.

But I need to find common sub-sets across all pages. For example, find the content that is common in pages 1-50, may be another subset that is common in pages 45,59,79,123,... another might be common in pages 450 - 459

Any better solution of finding such common sub-sets? Will it require creating trees?

Thanks.

Answer 1

It all really depends on "which" attributes you deem as "duplicated" or at least "common to a set".

You can do

$pages->aggregate(
  array(
    '$group' => array(
      '_id' => '$content',
      'pages' => array( '$push' => '$id' ),
      'count' => array( '$sum' => 1 )
    )
  )
);

Which is a lot more efficient that the client code you are using.

Or you can even do

$pages->aggregate(
  array(
    array( 
      '$project' => array(
        'title' => 1,
        'id' => 1,
        'contents' => 1,
        'types' => array( '$literal' => array( 'topic', 'parentTopic', 'text' ) )
      )
    ),
    array( '$unwind' => '$types' ),
      array(
        '$group' => array(
          '_id' => array( 
            'type' => '$types',
            'content' => array(
              '$cond' => array(
                array( '$eq' => array( '$types', 'topic' ) ),
                '$content.topic',
                array(
                  '$cond' =>  array(
                    array( '$eq' => array( '$types', 'parentTopic' ) ),
                    '$content.parentTopic',
                    '$content.text'
                  )
                )
              )
            )
          ),
          'pages' => array( '$push' => '$id' ),
          'count' => array( '$sum' => 1 )
        )
      )
    )
  )
);

Which groups by each sub-key.

All "grouping" is a form of 'set building'. But it's really not that clear what you are asking for here. Just trying to show something more efficient that what you seem to be doing.