Array Comparison in Php, and find the diff in values

Question

I want to compare two arrays in php. My arrays looks like this

Array ( 
[0] => Array ( [Id] => 1 [row1] => 1458)
[1] => Array ( [Id] => 2 [row1] => 16) 
[2] => Array ( [Id] => 3 [row1] => 115) 
[3] => Array ( [Id] => 4 [row1] => 18) 
[4] => Array ( [Id] => 5 [row1] => 13) 
[5] => Array ( [Id] => 6 [row1] => 13) 
[6] => Array ( [Id] => 7 [row1] => 131)
)

Array ( 
[0] => Array ( [Id] => 1 [row1] => 158)
[1] => Array ( [Id] => 2 [row1] => 165) 
[2] => Array ( [Id] => 3 [row1] => 111) 
[3] => Array ( [Id] => 4 [row1] => 186) 
[4] => Array ( [Id] => 5 [row1] => 3)
)

Firstly, array1 size and array2 sizes were not equal always. Id value in array1 may or may not present in array2, If the value is not present, function have to print the total index in array3, like

[someindex] => Array ( [Id] => 6 [row1] => 13 )

if it is present, function should subtract the row1 of array1 to row1 of array2 and print in array3, like this

[someindex] => Array ( [Id] => 1 [row1] => 1300)

and my final output should be,

Array ( 
[0] => Array ( [Id] => 1 [row1] => 1300)
[1] => Array ( [Id] => 2 [row1] => -149) 
[2] => Array ( [Id] => 3 [row1] => 4) 
[3] => Array ( [Id] => 4 [row1] => -168) 
[4] => Array ( [Id] => 5 [row1] => 10) 
[5] => Array ( [Id] => 6 [row1] => 13) 
[6] => Array ( [Id] => 7 [row1] => 131)
)

Can any one help me in solving this problem.

MDEV · Accepted Answer · 2013-08-12 10:29:33Z

1

$arr1 = Array ( 
    0 => Array ('Id' => 1, 'row1' => 1458)
    ,1 => Array ('Id' => 2, 'row1' => 16) 
    ,2 => Array ('Id' => 3, 'row1' => 115) 
    ,3 => Array ('Id' => 4, 'row1' => 18) 
    ,4 => Array ('Id' => 5, 'row1' => 13) 
    ,5 => Array ('Id' => 6, 'row1' => 13) 
    ,6 => Array ('Id' => 7, 'row1' => 131)
);
$arr2 = Array ( 
    0 => Array('Id' => 1, 'row1' => 158)
    ,1 => Array('Id' => 2, 'row1' => 165) 
    ,2 => Array('Id' => 3, 'row1'=> 111) 
    ,3 => Array('Id' => 4, 'row1' => 186) 
    ,4 => Array('Id' => 5, 'row1' => 3)
);
$final = array();
foreach($arr1 as $k => $sec)
{
    $sub = 0;
    foreach($arr2 as $sec2)
    {
        if($sec2['Id']==$sec['Id'])
        {
            $sub = $sec2['row1'];
            break;
        }
    }
    $sec['row1'] -= $sub;
    //Or to save to another element:
    //$sec['row2'] = $sec['row1']-$sub;
    $final[] = $sec;
}

echo '<pre>'.print_r($final,true).'</pre>';

Output:

Array ( 
    [0] => Array ( [Id] => 1 [row1] => 1300)
    [1] => Array ( [Id] => 2 [row1] => -149) 
    [2] => Array ( [Id] => 3 [row1] => 4) 
    [3] => Array ( [Id] => 4 [row1] => -168) 
    [4] => Array ( [Id] => 5 [row1] => 10) 
    [5] => Array ( [Id] => 6 [row1] => 13) 
    [6] => Array ( [Id] => 7 [row1] => 131)
)

edited Aug 12, 2013 at 10:29

answered Aug 12, 2013 at 9:44

MDEV

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6 Comments

Ja͢ck Over a year ago

@Sreenath Do note that the actual Id value is not being used for the lookup.

MDEV Over a year ago

@Sreenath Please note that my answer has been updated - as Jack quite rightly pointed out, this wasn't linking elements by the 'Id' element. It is now doing so correctly.

Ja͢ck Over a year ago

Modifying arrays in-place is a dangerous affair btw; what if you needed to use the old value of $arr1 again?

MDEV Over a year ago

@Jack Yea I originally wrote the code with a new $final array, but figured I'd change it to just modify the original unless the OP specified otherwise, so as to not use duplicate data (larger array sizes could lead to pointless increase in memory usage, if we start adding extra copies)

Sreenath Over a year ago

But I don't want to disturb the first array, I want the output in another array.

|

Ja͢ck · Accepted Answer · 2013-08-12 10:36:15Z

0

First, you either have to make the second array searchable by using the Id value as the keys or write a search function. I'm choosing the former:

$searchable = array_reduce($array2, function(&$result, $item) {
    return $result + array($item['Id'] => $item['row1']);
}, array());

The array_reduce() function starts with an empty array and builds it using the array addition operator; this creates an array that can be dereferenced using the id.

Then you perform a map operation on the first array:

$array3 = array_map(function($item) use ($searchable) {
    $value = isset($searchable[$item['Id']]) ? $searchable[$item['Id']] : 0;
    $item['row1'] -= $value;
//    $item['row2'] = $item['row1'] - $value;
    return $item;
}, $array1);

Doing a map operation preserves the original array and creates a new one with the values you choose inside a callback function.

edited Aug 12, 2013 at 10:36

answered Aug 12, 2013 at 9:54

Ja͢ck

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12 Comments

Sreenath Over a year ago

But, what if I had 10000 of records in my array? does it take time?

MDEV Over a year ago

@Sreenath My tests have shown that this method is 75% slower than mine. Average with the above = 0.145, average with mine = 0.083. Though to be fair, I'm not sure at what size the gaps really start to appear, so it depends on what size arrays you're using

Sreenath Over a year ago

But jack, What If I want to save in diff in row2?

Sreenath Over a year ago

SmokeyPHP, I don't know your name but I had a same question for you.

Ja͢ck Over a year ago

@Sreenath The time for 10k records is small; small enough to not matter :) if you want to save the difference in another field, simply change $item['row1'] -= $value; with $item['row2'] = $item['row1'] - $value;.

|

Iker Vázquez · Accepted Answer · 2013-08-12 09:37:34Z

0

Don't know if this exactly what you want, but you can check if a key exists with array_key_exists:

$array3 = array();
foreach ($array1 as $k => $v) {
        if (array_key_exists($k, $array2)) {
            $array3[] = $v - $array2[$k];
        } else {
            $array3[] = $v;
        }
    }

answered Aug 12, 2013 at 9:37

Iker Vázquez

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Comments

Expedito · Accepted Answer · 2013-08-12 09:56:32Z

This creates an indexing array ($new) in case the main keys don't match of in the original arrays.

$arr = array ( 
    0 => array ( 'Id' => '1','row1' => 1458),
    1 => array ( 'Id' => '2','row1' => 16),
    2 => array ( 'Id' => '3','row1' => 115),
    3 => array ( 'Id' => '4','row1' => 18),
    4 => array ( 'Id' => '5','row1' => 13),
    5 => array ( 'Id' => '6','row1' => 13),
    6 => array ( 'Id' => '7','row1' => 131));
$arr2 = array ( 
    0 => array ( 'Id' => '1','row1' => 158),
    1 => array ( 'Id' => '2','row1' => 165),
    2 => array ( 'Id' => '3','row1' => 111),
    3 => array ( 'Id' => '4','row1' => 186),
    4 => array ( 'Id' => '5','row1' => 3));
$new = array();
foreach ($arr2 as $key => $value){
    $new[$value['Id']] = $value['row1'];
}
foreach ($arr as $key => $value){
    if (isset($new[$value['Id']])){
        $arr[$key]['row1'] -= $new[$value['Id']];
    }
}
print_r($arr);

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