PHP 1:1 到 1:many 数组

Question

我有三个数组，分别称为 associativeArray keyArray 和 valueArray。 associativeArray 是一个由键/值对组成的数组，这些对被拆分并放入keyArray 和valueArray。我现在要做的是创建一个名为newArray 的第四个数组，它使用valueArray 中的元素作为其键，并且值来自它们各自的keyArray。但与具有 1:1 键值对的 associativeArray 不同，我希望 newArray 具有 1:many 键值对，而没有任何重复键。这是我为它编写的代码：

foreach($keyArray as $keyElement){
    $valueElement = $associativeArray[$keyElement];
    if (!in_array($valueElement,$newArray)){
        array_push($newArray, $valueElement => array($keyElement));
    }
    else{
        array_push($newArray[$valueElement],$keyElement);
    }
}

但是每当我运行它时，我都会得到：

PHP Parse error:  syntax error, unexpected T_DOUBLE_ARROW

Answer 1

您不需要所有这些数组。只需associativeArray 就足够了。

你可以这样做：

$newArray = array();
// This will loop in the array so that, in each step:
//  - $k is the current key
//  - $v is the current value
foreach($associativeArray as $k => $v) {
    // If newArray doesn't already have $v as a key
    if (!array_key_exists($v, $newArray)) {
        // Define it as a new array with only one element
        $newArray[$v] = array($k);        
    } else {
        // If it already exists, just push $k to it's elements
        $newArray[$v][] = $k; // This is the same as array_push($newArray[$v], $k)
    }
}

Answer 2

最简单的解决方案可能是这样的

foreach( $keyArray as $key )
{
  // get the value from the associative array
  $value = $associativeArray[ $key ];

  // check if the key was set before into $newArray
  // if you don't check and initialize it, you'll get an error
  // when you try to add new elements
  if( !array_key_exists( $key, $newArray ) )
  {
       $newArray[ $key ] = array();
  }

  // To prevent duplicated ( like you have in your code ) 
  // you just have to check if the element is in the $newArray
  if ( !in_array( $value, $newArray[ $key ] ) )
  {
      $newArray[ $key ][] = $value; // if you wanna use array_push --> array_push( $newArray[ $key ], $value );
  }
}

但是，这取决于您的目标，我会使用引用重写 associativeArray 并将值转换为数组。那时你不需要这 3 个额外的数组，只需要 associativeArray 和一行代码

// this will cast each value of the array. Since
// the value is referenced the array will be updated.
// You don't have to check for duplicated value because it was an 
// array 'key' => 'val' so it is not possible to have multiple values 
// with the same key
foreach( $associativeArray as $key => &$val )
{
   $val = (array) $val;
}