def split_groups(Y):
    """Split the retweet amounts in Y into buckets.
    
    Bucket 0 - 0 retweets.
    Bucket 1 - 1 < retweets <= 10.
    Bucket 2 - 11 < retweets <= 50.
    Bucket 3 - More than 50 retweets.
    """
    Ysplit = []
    for y in Y:
        if y == 0:
            Ysplit.append(0)
        elif y <= 10:
            Ysplit.append(1)
        elif y <= 50:
            Ysplit.append(2)
        else:
            Ysplit.append(3)
    return Ysplit