csvを2次元配列に読み込む

<?php
        $file_name = "data.csv";
        $fp = fopen( $file_name, 'r' );
        $data = array();
        while( $ret_csv = fgetcsv( $fp, 256 ) ){
                for($col = 0; $col < count( $ret_csv ); $col++ ){
                        $data[$col][$row] = $ret_csv[$col];
                }
                $row++;
        }
        fclose( $fp );
?>

＜data.csv＞

2369,1467
509,463
479,298
859,649
391,284

配列の中身

$data[0][1]=[2369]
$data[1][1]=[1467]
$data[0][2]=[509]
$data[1][2]=[463]
$data[0][3]=[479]
$data[1][3]=[298]
$data[0][4]=[859]
$data[1][4]=[649]
$data[0][5]=[391]
$data[1][5]=[284]