$b = $a["vorname"];//oder $b = $a[1];
<?php$wochentage = array("so" => "Sonntag","mo" => "Montag","di" => "Dienstag","mi" => "Mittwoch","do" => "Donnerstag","fr" => "Freitag","sa" => "Samstag");?> echo $wochentage[2];
<?php$array = array( 'nachname' => '', 'vorname' => '' );print_r(array_slice($array, 1, 1));// Array ( [vorname] => ) ?>