@sortedCollectionData = sort {
    $collectionData[ $b ]{CollectionId} <=> $collectionData[ $a ]{CollectionId}
    ||
    $collectionData[ $b ]{Modified} cmp $collectionData[ $a ]{Modified}
    } 0 .. $#collectionData;

##</code><code>##

    @sortedCollectionData = sort {
    $b->{CollectionId} <=>  $a->{CollectionId}
    ||
    $b->{Modified} cmp $a->{Modified}
    } @collectionData;