寻找在PHP数组的子集 [英] Finding the subsets of an array in PHP

问题描述

我有属性的关系模式（A B C D）。
我有一组函数依赖我了。

I have a Relational Schema with attributes (A B C D). I have a set of Functional Dependencies with me too.

现在我需要确定对R的属性的所有可能的子集的关闭。这就是我卡住了。我需要学习如何在PHP中找到的子集（不重复）。

Now I need to determine the closure for all the possible subsets of R's attributes. That's where I am stuck. I need to learn how to find subsets (non-repeating) in PHP.

我的数组存储这样。

$ATTRIBUTES = ('A', 'B', 'C', 'D').

所以我的子集应

$SUBSET = ('A', 'B', 'C', 'D', 'AB', 'AC', AD', 'BC', 'BD', 'CD', 'ABC', 'ABD', 'BCD', 'ABCD')

在code不应该是一件大事，但由于某种原因，我不能让我的头周围。

The code shouldn't be something big but for some reason I can't get my head around it.

推荐答案

您希望为电力集 $属性？那是你的问题意味着什么。

You wish for the power set of $attributes? That is what your question implies.

一个例子可以发现这里（引用完整性）

An example can be found here (quoted for completeness)

<?php 
/** 
* Returns the power set of a one dimensional array, a 2-D array. 
* [a,b,c] -> [ [a], [b], [c], [a, b], [a, c], [b, c], [a, b, c] ]
*/ 
function powerSet($in,$minLength = 1) { 
   $count = count($in); 
   $members = pow(2,$count); 
   $return = array(); 
   for ($i = 0; $i < $members; $i++) { 
      $b = sprintf("%0".$count."b",$i); 
      $out = array(); 
      for ($j = 0; $j < $count; $j++) { 
         if ($b{$j} == '1') $out[] = $in[$j]; 
      } 
      if (count($out) >= $minLength) { 
         $return[] = $out; 
      } 
   } 
   return $return; 
} 

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