Format a set of dates (timestamps) into a format like 1, 2, 3 Jan, 13 Feb, 15 Mar 2011

format_dates.php

<?php
 function formatDates( $dates ) {

    $output = '';
    $month = '';
    $year = '';

    sort( $dates, SORT_NUMERIC );

    foreach ( $dates as $date ) {
      $date = floatval( $date );
      if( date(' M, ' , $date) != $month ) {
        $output = rtrim( $output, ', ' ) . $month;
        $month = date( ' M, ' , $date );
      }
      if( date(' Y, ', $date) != $year ) {
        $output = rtrim( $output, ', ' ) . $year;
        $year = date( ' Y, ' , $date );
      }

      $output .= date('j, ', $date );
    }

    $output = rtrim( $output, ', ') . rtrim( $month, ', ' ) . rtrim( $year, ', ' );

    return $output;
  }
?>