PHP splitting arrays into groups based on equal values

<?php
//the array
$data = array(array(2,'Department of General Chemistry'),array(3,'Institute of Silicate Materials'),array(4,'Department of General Chemistry'),array(5,'Department of General Chemistry'),array(6,'Institute of Silicate Materials'));

//a new array to store the data    
$newData = array();

//loop over each value in the data
foreach($data as $d){
    //check if a key exists under the new data for the common value (affiliation)
    if(!isset($newData[$d[1]])){
        //doesn't exist, group under the common value (affiliation)
        $newData[$d[1]] = array(array(),$d[1]);
    }
    //add the author under it's affiliation
    $newData[$d[1]][0][] = $d[0];
}

//get the values from the new data, this resets the keys
$newData = array_values($newData);

//display the data
echo '<pre>'.print_r($newData,1).'</pre>';

example

results in:

Array
(
    [0] => Array
        (
            [0] => Array
                (
                    [0] => 2
                    [1] => 4
                    [2] => 5
                )

            [1] => Department of General Chemistry
        )

    [1] => Array
        (
            [0] => Array
                (
                    [0] => 3
                    [1] => 6
                )

            [1] => Institute of Silicate Materials
        )

)

Try this code , it should solve your problem:

<?php
$element = array ( 
    array ( 
            2 
            ,'Department of General Chemistry'
        ) ,
    array ( 
            3, 
            'Institute of Silicate Materials'
        ), 
    array ( 
            4 
            , 'Department of General Chemistry'
        ) ,
    array ( 
            5 
            , 'Department of General Chemistry'
        ) ,
    array ( 
            6 
            , 'Institute of Silicate Materials'
        ) 
);

$res = array();

for($i=0; $i< count($element); $i++){
    $res[$element[$i][1]][] =  $element[$i][0];
}

echo '<pre>';
    var_dump($res);
echo '</pre>';

foreach ($res as $key => $value){
    echo $key .' : '. implode(',',$value). '<br>';
}
?>

You can do it like this:

$ar = array ( 
    array( 
        2,
        'Department of General Chemistry'
    ),
    array( 
        3,
        'Institute of Silicate Materials'
    ),
    array( 
        4,
        'Department of General Chemistry'
    ),
    array( 
        5,
        'Department of General Chemistry'
    ), 
    array( 
        6,
        'Institute of Silicate Materials'
    )
);

$result = array();
foreach ($ar as $key => $value) {
    if (array_key_exists($value[1], $result)) {
        $result[$value[1]] .= ',' . $value[0];
    } else {
        $result[$value[1]] = $value[0];
    }
}

foreach ($result as $key => $value) {
    echo $value . ' ' . $key . '<br>';
}