<?php
$variavel = "2:2014-07-13,4:2014-08-13,6:2014-08-13,7:2014-08-13";
$var = explode(",", $variavel);
$total_var = count($var);
$n = 0;
while($n < $total_var){
    $var[$n];

    while($n < $total_var){
        $explode2 = explode(":", $var[$n]);
        $explode2 = $explode2[0];
        print $explode2; //Result: 2467 | How would: 2,4,6,7
    $n++;
    }
$n++;
}
?>