check if array is in two multidimensional array

Question

I have two multidimensional arrays:

Haystack

$haystack = array (
  0 => array (
    "child_element_id" => 11
    "answer_id" => 15
  ),
  1 => array (
    "child_element_id" => 12
    "answer_id" => 17
  ),
  2 => array (
    "child_element_id" => 13
    "answer_id" => 21
  )
)

Needle

 $needle = array (
  0 => array (
    "child_element_id" => 12
    "answer_id" => 17
  ),
  1 => array (
    "child_element_id" => 13
    "answer_id" => 21
  )
)

I want to check if all the key values from array "Needle" exists in the array "Haystack". What's the best practice for this? Thank you!

Does Needle has constant key name?

Mohammad
– Mohammad

2017-01-08 16:20:24 +00:00
Commented Jan 8, 2017 at 16:20 — Mohammad
– Mohammad, Commented Jan 8, 2017 at 16:20
Sorry, yes it does "child_answers" to be precise

Lex Hartman
– Lex Hartman

2017-01-08 16:21:25 +00:00
Commented Jan 8, 2017 at 16:21 — Lex Hartman
– Lex Hartman, Commented Jan 8, 2017 at 16:21

Carsten Massmann · Accepted Answer · 2017-01-08 18:12:29Z

2

almost a solution:
@shalvah gave a good starting point. However, in the suggested solution he forgot to loop over the elements of the $needle array like shown below:

function array_in_array($neearr,$haystack) {
  foreach ($neearr as $needle){
    foreach ($haystack as $array) {
      //check arrays for equality
      if(count($needle) == count($array)) {
        $needleString = serialize($needle);
        $arrayString = serialize($array);
        echo "$needleString||$arrayString<br>";
        if(strcmp($needleString, $arrayString) == 0 ) return true;
      }
      return false;
    }
  }
}

But even so is this not completely "water tight". In cases where elements of the "needle" arrays appear in a different order (sequence) the serialze()-function will produce differing strings and will lead to false negatives, like shown in the exampe below:

$hay=array(array('a'=>'car','b'=>'bicycle'),
         array('a'=>'bus','b'=>'truck'),
         array('a'=>'train','b'=>'coach'));

$nee1=array(array('a'=>'car','b'=>'bicycle'),
         array('a'=>'train','b'=>'coach'));

$nee2=array(array('b'=>'bicycle','a'=>'car'),  // different order of elements!
         array('a'=>'train','b'=>'coach')); 

echo array_in_array($nee1,$hay); // true
echo array_in_array($nee2,$hay); // false (but should be true!)

a slightly better solution
This problem can be solved by first sorting (ksort(): sort by key value) all the elements of all the "needle" arrays before serialize-ing them:

function array_in_array($neearr,$haystack) {
  $haystackstrarr = array_map(function($array){ksort($array);return serialize($array);},$haystack);
  foreach ($neearr as $needle){
    ksort($needle);
    $needleString = serialize($needle);
    foreach ($haystackstrarr as $arrayString){
      if(strcmp($needleString, $arrayString) == 0 ) return true;
    }
    return false;
  }
}

echo array_in_array($nee1,$hay); // true
echo array_in_array($nee2,$hay); // true

edited Jan 8, 2017 at 18:12

answered Jan 8, 2017 at 17:43

Carsten Massmann

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3 Comments

Daryl Gill Over a year ago

Would it not be easier to recursively call the function? passing the processed data as a secondary attribute?

Carsten Massmann Over a year ago

@DarylGill: Quite right! Even though I did some sorting in my code it will most likely not work reliably with deeper "needle" arrays. This was just a "quick shot" done on the basis of shalvahs's post. A recursive code is very likely the better approach. Maybe, you can put together a little example ;-) ...

shalvah Over a year ago

@cars10 looping over the needle array? Isn't $nearr 1D while $haystack 2D?

AbraCadaver · Accepted Answer · 2017-01-09 03:05:02Z

Pretty easy using in_array() since needle can be an array:

$found = 0;
foreach($needle as $array) {
    if(in_array($array, $haystack, true)) {
        $found++;
    }
}
if($found === count($needle)) {
    echo 'all needles were found in haystack';
}

Or maybe:

$found = true;
foreach($needle as $array) {
    if(!in_array($array, $haystack, true)) {
        $found = false;
        break;
    }
}
if($found) {
    echo 'all needles were found in haystack';
}

You could even use array_search() as you can use an array for needle as well, no need to run two loops.

Using serialize():

if(count(array_map('unserialize',
         array_intersect(array_map('serialize', $needle), 
                         array_map('serialize',$haystack)))) == count($needle))
{
                             echo 'all needles were found in haystack';
}

serialize() the inner arrays of both arrays and compute the intersection (common inner arrays)
unserialize() the result and compare the count() with the count of $needle

shalvah · Accepted Answer · 2017-01-10 07:27:52Z

1

You could use this function:

function array_in_array(array $needle, array $haystack) {
foreach($needle as $nearr) {
  foreach ($haystack as $array) {
    //check arrays for equality
    if(count($needle) == count($array)) {
      $needleString = serialize($needle);
      $arrayString = serialize($array);
      if(strcmp($needleString, $arrayString) == 0 )
        return true;
      }
}
  return false;
}

edited Jan 10, 2017 at 7:27

answered Jan 8, 2017 at 16:49

shalvah

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