Finding the intersections of array and create a new set of arrays

Question

Im looking the build a new array by finding the intersection of a given array of arrays.

This probably a simple set theory problem for most people but its kind of hard for me to wrap my head around.

So I have a keyed array:

$myArray = [
 'array1' => [A, B, C],
 'array2' => [A, B, C, D],
 'array3' => [A, B, C, D],
 'array4' => [D],
]

And the goal is to build an entirely new array keyed in with concatenated keys of the previous array if they have an intersection:

Basically like this:

 $newArray = [
   'array1,array2,array3' => [A, B, C],
   'array2,array3,array4' => [D]
  ]

Since array1, array2, array3 have ABC in command they will form as one keyed array, same as array2,array3,array4 and so on.

I have tried to experiment with array_intersect but it seems like its not the one that im looking for or perhaps I solving it in a really wrong way. Any ideas is much appreciated.

$myArray = [
 'array1' => [A, B, C],
 'array2' => [A, B, C, D],
 'array3' => [A, B, C, D],
 'array4' => [D],
];


$newArray = [];
$keys = array_keys($myArray);

for($i = 0, $size = count($myArray); $i < $size; $i++){
  for($k = $i; $k < $size; $k++){
      print_r(array_intersect($myArray[$keys[$i]], $myArray[$keys[$k]]));    
   }
}

  //Foal 
  // 'array1,array2,array3' => [A, B, C]
  // 'array2,array3,array4' => [D]

The question is not completely defined. Shouldn't $newArray also contain the key 'array1,array4' with value [] and the key 'array2,array3' with value [A, B, C, D] etc? — axiac
– axiac, Commented Aug 7, 2017 at 19:44
array2,array3 is not included since all of its elements exist in already in array1, array2, array3 and array2,array3,array4, although in set theory an empty set is also considered a new entry — XDProgrammer
– XDProgrammer, Commented Aug 7, 2017 at 19:52

Ravinder Reddy · Accepted Answer · 2017-08-07 19:45:18Z

2

This code will give the desired array as output.

$myArray = [
 'array1' => ['A', 'B', 'C'],
 'array2' => ['A', 'B', 'C', 'D'],
 'array3' => ['A', 'B', 'C', 'D'],
 'array4' => ['D'],
];
// Define new arrays
$newArray = [];
$finalArray = [];

// loop the array and create a new array with values like (A,B,C..) as keys 
foreach($myArray as $key=>$value){
    foreach($value as $k=>$v){
        // if already value exists append new value with comma
        $newArray[$v] = isset($newArray[$v]) ? $newArray[$v].','.$key:$key;
    }
}
foreach($newArray as $key=>$value){
        $finalArray[$value][] = $key;

}
print_r($finalArray);

Out put is

Array
(
    [array1,array2,array3] => Array
        (
            [0] => A
            [1] => B
            [2] => C
        )

    [array2,array3,array4] => Array
        (
            [0] => D
        )

)

edited Aug 7, 2017 at 19:45

answered Aug 7, 2017 at 19:43

Ravinder Reddy

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1 Comment

XDProgrammer Over a year ago

That is impressive,! Thank you

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