That's fairly easy: 
# Pseudocode!
foreach $date (@dates) {
    split $date into $year,$month,$day
    push(@{$dates{$year}->{$month}}, $day);
}

[download]
s$$([},&%#}/&/]+}%&{})*;#$&&s&&$^X.($'^"%]=\&(|?*{%
+.+=%;.#_}\&"^"-+%*).}%:##%}={~=~:.")&e&&s""`$''`"e

In reply to Re^3: putting dates int year, month date by Skeeve
in thread putting dates int year, month date by Anonymous Monk

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