How can I combine two array by mapping value in php?

Solution:

This should work, also if there's no price for an item in the array $b then the default price 0 will be added.

<?php

$result = [];

$t = array_column($b, 'a_id');

foreach($a as $k => $v) {
    
    $index = array_search($v['id'], $t);
    $v['price'] = $index !== FALSE ? $b[$index]['price'] : 0;
    $result[] = $v;

}

print_r($result);

?>
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Result:

(
    [0] => Array
        (
            [name] => Apple
            [id] => 1
            [price] => 30
        )

    [1] => Array
        (
            [name] => Banana
            [id] => 2
            [price] => 20
        )

    [2] => Array
        (
            [name] => orange
            [id] => 3
            [price] => 10
        )
)
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Solution:

You can use this code

$result = [];

for($i=0; $i<sizeof($a); $i++){
    if(array_key_exists($i,$b)){
        $b[$i]['id']=$b[$i]['a_id'];
        unset($b[$i]['a_id']);
    }
    $result[] = array_merge($a[$i], array_key_exists($i,$b)?$b[$i]:array());
}

print_r($result);
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Solution:

You can do it as follows:

foreach($a as $k => $item)
{        
    $price = 0;    

    foreach($b as $priceItem)
    {
       if($priceItem['a_id'] === $item['id'])
       {
            $price = $priceItem['price'];
            break;
       }   
    }

    $a[$k]['price'] = $price;
}
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However, this isn't too efficient as every new price and item will exponentially increase the loops required.

If you are able to use the product IDs as the key in your first array, you could do it a lot more efficiently:

// Key $a by product ID
$a = [
    1 => [
        'name'=>'Apple',
        'id' => 1
    ],
    2 => [
        'name'=>'Banana',
        'id' => 2
    ],
    3 => [
        'name' => 'orange',
        'id' => 3
    ]
];

foreach($b as $priceItem)
{   
    $a[$priceItem['a_id']]['price'] = $priceItem['price'];
}
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Solution:

Not that this is more efficient, but maybe a bit more flexible, and readable. Its on you!

<?php

$a = [
    '0' => ['name'=>'Apple', 'id' => 1],
    '1' => ['name'=>'Banana', 'id' => 2],
    '2' => ['name' => 'orange', 'id' => 3],
    '3' => ['name' => 'extra', 'id' => 4]
];
$b = [
    '0' => ['price'=> 20, 'a_id' => 2],
    '1' => ['price'=> 10, 'a_id' => 3],
    '3' => ['price'=> 30, 'a_id' => 1]
];

$lookup = [];
foreach($b as $k => $v) {
    if (array_key_exists($v['a_id'], $lookup)) {
        // you have multiple prices... do something, throw an error, log an error, overwrite the value
        // what ever you want
    } else {
        // in case you have multiple array items you want to copy over
        // you can later merge the array
        // if its only ever going to be prices , you can just take the price instead of the unset
        $parent_id = $v['a_id'];
        unset($v['a_id']);
        $lookup[$parent_id] = $v;
    }
}

// in case you have more values that you want push, if nothing exists
$default_values = ['price' => 0];

foreach($a as $k => &$v) {

    if (array_key_exists($v['id'], $lookup)) {
        $v = array_merge($v, $lookup[$v['id']]);
    } else {
        $v = array_merge($v, $default_values);
    }

} 
/* bit less readable
foreach($a as $k => &$v)
    $v = array_merge($v, array_key_exists($v['id'], $lookup) ? $lookup[$v['id']] : $default_values);
*/
print_r($a);
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result

Array
(
    [0] => Array (
        [name] => Apple [id] => 1 [price] => 30
    )
    [1] => Array (
        [name] => Banana [id] => 2 [price] => 20
    )
    [2] => Array (
        [name] => orange [id] => 3 [price] => 10
    )
    [3] => Array (
        [name] => extra [id] => 4 [price] => 0
    )
)
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