php unable to update specific array value

Question

I am trying to compare two arrays and update specific array values based on conditions.

Getting attendance array of absent students:

$array1 = 
    array(
    array("student_id" => "2",
        "date" => "2016-04-24"),
    array("student_id" => "6",
        "date" => "2016-04-24"));
$attendance = json_decode(json_encode($array1));

Getting student list array of all students:

$array2 = 
    array(
    array("student_id" => "1",
        "Reason" => "",
        "date" => "2016-04-24"),
    array("student_id" => "2",
        "Reason" => "",
        "date" => "2016-04-24"),
    array("student_id" => "3",
        "Reason" => "",
        "date" => "2016-04-24"),
    array("student_id" => "6",
        "Reason" => "1",
        "date" => "2016-04-24"));
$students = json_decode(json_encode($array2));

Taking out only student IDs of absent students:

foreach($attendance as $att) 
{   $atts[] = $att->student_id;}

Here I am trying to find out if any of the students ID in student array matches with ID in absent array. If ID is present then I will update the Reason as "1". Else will make the reason as 0

for ($i = 1; $i <= count($students); $i++) {
    if(in_array($atts[$i],$students))
    {
        $students->Reason='1';
    }
    else
    {
        $students->Reason='0';
    }
} 
echo '<pre>',print_r($students,1),'</pre>';

Here I am unable to update student array with "reason" values.

Hey Jon I am new to php and and was trying to convert multi dimensional array to array of std objects — Ash
– Ash, Commented Apr 28, 2016 at 10:11
Okay, first off, just use the arrays. You have no benefit in this use-case of converting to objects. 2) $students is an array, not an object, so doing $students->Reason doesn't even make sense as you're actually wanting to update $students[$i]? 3) $students is an array of either more arrays, or currently in your case, objects. Your in_array is currently trying to compare a scalar value (an ID) against an array or object, which isn't going to match. — Jonnix
– Jonnix, Commented Apr 28, 2016 at 10:13
I usually wouldn't do this, but I've done a little cleaning up and refactoring to what I believe works the way you want (see 3v4l.org/b5fce). It's only an example using your code as a basis. Please have a read and understand what the differences and changes are before using :). — Jonnix
– Jonnix, Commented Apr 28, 2016 at 10:24

zken · Accepted Answer · 2016-04-29 07:29:26Z

1

If you just want to compare student_id from array1 with student_id from array2, and set Reason in array2 if they correspond to each other, use this :

foreach ($array1 as $key1 => $value1) {
    foreach ($array2 as $key2 => $value2) {
        if ($value1['student_id'] == $value2['student_id']) {
            $array2[$key2]['Reason'] = 1;
        } else if ($array2[$key2]['Reason'] != 1) {
            $array2[$key2]['Reason'] = 0;
        }
    }
}

edited Apr 29, 2016 at 7:29

answered Apr 28, 2016 at 10:59

zken

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4 Comments

Ash Over a year ago

when I am increasing array elements in both arrays, the code doesnt work

zken Over a year ago

Did you increase with another array ? Show me what you have now

Ash Over a year ago

I have made changes in my original question. Added arrays in both array1 and array2

zken Over a year ago

My bad, I modified my post.

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