Multidimenssion array compare two arrays and update first array value

Question

I want to filter a array by a number and update its status in the first array.

I have two array $arr1,$arr2

$arr1 = array(
    0=>array('number'=>100,name=>'john'),
    1=>array('number'=>200,name=>'johnny')
);
$arr2= array(
    0=>array('number'=>300,name=>'r'),
    1=>array('number'=>100,name=>'b'),
    2=>array('number'=>200,name=>'c')
);

Final output should be an array like this

$arr1 = array(
    0=>array('number'=>100,name=>'b'),
    1=>array('number'=>200,name=>'c')
);

Any ideas to start off please ?

How are you retrieving this data? Because it would be a heck of a lot simpler if you have meaningful keys instead of having to inspect the number part... — Wrikken
– Wrikken, Commented May 15, 2013 at 18:36
Based on the number from second array update the name part of first array. — mark rammmy
– mark rammmy, Commented May 15, 2013 at 18:38
That's not what I'm asking. I'm asking whether we can simplify this problem at the source rather then do some redundant loops later. — Wrikken
– Wrikken, Commented May 15, 2013 at 18:39
@RobertPodwika array_intersect($arr1, $arr2) wouldn't work here, it does a naive string comparison. It would either include all elements from both arrays, or none. array-uinstersect with a custom comparison would get closer, but it wouldn't transform the first array. OP doesn't specify what he wants to do with elements in the $arr1 but not in $arr2, but the implication is that they would remain in $arr1, where as intersection would remove them. — Patrick M
– Patrick M, Commented May 15, 2013 at 19:05

Patrick M · Accepted Answer · 2013-05-15 18:55:25Z

For specialized array modifications like this, the method of choice is array walk. It allows you to apply a custom function to each element in a given array.

Now, because of your data format, you will have to do a loop. Wrikken is asking if you can retrieve or transform the data to provide faster access. The algorithm below is O(n^2): it will require as many cycles as there are elements in the first array times the number of elements in the second array, or exactly count($arr1) * count($arr2).

function updateNameFromArray($element, $key, $arr2) {
    foreach($arr2 as $value) {
        if($value['number'] == $element['number']) {
            $element['name'] == $value['name'];
            break;
        }
    }
}

array_walk($arr1, "updateNameFromArray", $arr2);

Now, what Wrikken is suggesting is that if your arrays can be changed to be keyed on the 'number' property instead, then the search/replace operation is much easier. So if this were your data instead:

$arr1 = array(
    100=>array('number'=>100,name=>'john'),
    200=>array('number'=>200,name=>'johnny')
);
// notice the keys are 100 and 200 instead of 0,1

$arr2= array(
    300=>array('number'=>300,name=>'r'),
    100=>array('number'=>100,name=>'b'),
    200=>array('number'=>200,name=>'c')
);
// notice the keys are 300, 100 and 200 instead of 0,1, 2

Then you could do this in O(n) time, with only looping over the first array.

foreach($arr1 as $key => $value) {
    if(isset($arr2[$key])) {
        $value['number'] = $arr2[$key]['number'];
    }
}

ROMMEL · Accepted Answer · 2013-05-15 18:57:11Z

2

Try this. It's not that clean but i think it would work.

<?php

 $arr1 = array(0=>array('number'=>100,'name'=>'john'),1=>array('number'=>200,'name'=>'johnny'));
 $arr2= array(0=>array('number'=>300,'name'=>'r'),1=>array('number'=>100,'name'=>'b'),2=>array('number'=>200,'name'=>'c'));
 foreach( $arr1 as $key=>$data1 )
  {
foreach( $arr2 as $key2=>$data2 )
{
    if( $data1['number'] == $data2['number'] )
    {
        $arr1[$key]['name'] = $arr2[$key2]['name'];
    }
 }

  }
 print_r( $arr1 );
?>

the output would be :

Array
(
[0] => Array
    (
        [number] => 100
        [name] => b
    )

[1] => Array
    (
        [number] => 200
        [name] => c
    )

)

answered May 15, 2013 at 18:57

ROMMEL

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Comments

Brian Moore · Accepted Answer · 2013-05-15 18:53:17Z

There isn't really a simple way for this to be accomplished with generic PHP functions, so, You might need to create mapping arrays.

The way I would approach this, is creating a loop that goes through the first array, and maps the number value as a key to the index of it's place in $arr1 giving you:

$tmp1 = array();
foreach ($arr1 as $key => $number_name) {
  $tmp1[$number_name['number']] = $key;
}

This should give you an array that looks like

$tmp1 [
  100 => 0,
  200 => 1
];

Then I would loop through the second array, get the number value, if that existed as a key in $tmp1, get the associated value (being the key for $arr1), and use that to update the name in $arr1.

// Loop through $arr2
foreach ($arr2 as $number_name) {
  // Get the number value
  $number = $number_name['number'];

  // Find the $arr1 index 
  if (isset($tmp1[$number])) {
    $arr1_key = $tmp1[$number];
    // Set the $arr1 name value
    $arr1[$arr1_key]['name'] = $number_name['name'];
  }
}

Matanya · Accepted Answer · 2013-05-15 19:37:18Z

<?php 

//Set the arrays

$arr1 = array(
    array('number'=>100,'name'=>'john'),
    array('number'=>200,'name'=>'johnny')
);

$arr2= array(
    array('number'=>300,'name'=>'r'),
    array('number'=>100,'name'=>'b'),
    array('number'=>200,'name'=>'c')
);

// use a nested for loop to iterate and compare both arrays

for ($i=0;$i<count($arr1);$i++):

    for ($j=0;$j<count($arr2);$j++):

        if ($arr2[$j]['number']==$arr1[$i]['number'])
            $arr1[$i]['name']=$arr2[$j]['name'];

    endfor;

endfor;

print_r($arr1);

OUTPUT:

 Array (
 [0] => Array ( [number] => 100 [name] => b )
 [1] => Array ( [number] => 200 [name] => c )
 )

That being said, you should probably reconsider the very way your data is structured. Do you really need a multi-dimensional array or can you use a simple associative array, like so:

 // set the arrays

 $arr1 = array(
        'john'=>100,
        'johnny'=>200          
    );

 $arr2 = array(
       'r'=>300,
       'b'=>100,
       'c'=>200
     );

// find values in arr2 common to both arrays

$arr3 = array_intersect($arr2, $arr1);

// change the key of arr1 to match the corresponding key in arr2

  foreach ($arr3 as $key=>$value) {

      $old_key = array_search($value, $arr1);
      $arr1[$key]=$arr1[$old_key];
      unset($arr1[$old_key]);

  }


print_r($arr1);

OUTPUT:

Array ( 
   [b] => 100 
   [c] => 200 
)

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