<?php

$memberships = array(); // Your multi-dimensional array
$memberships[0] = array('Group A','something else');
$memberships[1] = array('Group B','something else');
$memberships[2] = array('Group B','something else');
$memberships[3] = array('Group A','something else');
$memberships[4] = array('Group A','something else');
    
    foreach($memberships as $membership)
    {
       $count[$membership[0]]++;
    }

var_dump($count);

?>