How to update specific key's value in an associative array in PHP?

I've a following associative array named $data

Array
(
    [0] => Array
        (
            [transaction_user_id] => 359691e27b23f8ef3f8e1c50315cd506
            [transaction_no] => 19500912050218
            [transaction_total_amount] => 589.00
            [transaction_date] => 1335932419
            [transaction_status] => cancelled
        )

    [1] => Array
        (
            [transaction_user_id] => 9def02e6337b888d6dbe5617a172c18d
            [transaction_no] => 36010512050819
            [transaction_total_amount] => 79.00
            [transaction_date] => 1336476696
            [transaction_status] => cancelled
        )

    [2] => Array
        (
            [transaction_user_id] => 9def02e6337b888d6dbe5617a172c18d
            [transaction_no] => 19020512050820
            [transaction_total_amount] => 299.00
            [transaction_date] => 1336476739
            [transaction_status] => cancelled
        )

    [3] => Array
        (
            [transaction_user_id] => 9def02e6337b888d6dbe5617a172c18d
            [transaction_no] => 27050512050821
            [transaction_total_amount] => 79.00
            [transaction_date] => 1336476927
            [transaction_status] => cancelled
        )

    [4] => Array
        (
            [transaction_user_id] => 8e9050a3646c98342b9ba079fba80982
            [transaction_no] => 12070512050822
            [transaction_total_amount] => 129.00
            [transaction_date] => 1336477032
            [transaction_status] => cancelled
        )

)

and I want to convert the value of key [transaction_date] into user readable format (i.e. mm/dd/yyyy). For that I written the following code in a function which returns the whole array:

 foreach($data as $value)
 {
   	$value[transaction_date]=date('d/m/Y',$value[transaction_date]);
 }
    
 return $data;

My problem is I'm getting the same array without changing the value of [transaction_date] for all the array elements. Actually array with updated values for [transaction_date] is expected to be returned. Can anyone help me out to resolve this issue? Thanks in advance.

Change your foreach to something like this, You are not assigning data back to your return variable $data after performing operation on that.

foreach($data as $key => $value)
{
  $data[$key]['transaction_date'] = date('d/m/Y',$value['transaction_date']);
}

Codepad DEMO.

This will work too!

foreach($data as &$value) {
  $value['transaction_date'] = date('d/m/Y', $value['transaction_date']);
}

Yay for alternatives!

PHP array_walk() function is specifically for altering array.

Try this:

array_walk ( $data, function (&$key) { 
    $key["transaction_date"] = date('d/m/Y',$key["transaction_date"]); 
});

Use array_walk_recursive function for multi-denominational array.

array_walk_recursive($data, function (&$v, $k) { 
    if($k == 'transaction_date'){ 
        $v = date('d/m/Y',$v); 
    } 
});

The best approach is using a lambda within "array_walk" native function to make the required changes:

    array_walk($data, function (&$value, $key) {
            if($key == 'transaction_date'){ 
                  $value = date('d/m/Y', $value); 
            }
    });

The value is updated in the array as it's passed with as a reference "&".

This a single solution, in where your_field is a field that will set and new_value is a new value field, that can a function or a single value

foreach ($array as $key => $item) {
   $item["your_field"] = "new_value";
   $array[$key] = $item;
}

In your case new_value will be a date() function

foreach($data as $value)
{
    $value["transaction_date"] = date('d/m/Y',$value["transaction_date"]);
}
return $data;