def split_data(data):
    """
        Split lines of a previously loaded dataset into 4 separeted lists.
        Example: [[word][tag1][tag2][tag3]] -> [word][tag1][tag2][tag3]
        
        :param data: data to split. Must be in matrix format (see load_data).
        :return four arrays: The first one contains sentences (one array of words per sentence) and the other threes are arrays of tags.
    """
    
    # Init return lists (4 return values)
    # 0: words, 1: tag1, 2: tag2, 3: tag3
    return_list = [[],[],[],[]]
    
    # Iterate each row
    for row in data:
        # Iterate each attribute of row (words, tag1, tag2, tag3)
        for i in range(4):
            tmp_list = []
            # collect each element of the current attribute i of the current row
            for element in row[i]:
                tmp_list.append(element)
            return_list[i].append(tmp_list)
            
    return return_list