def mapper(chunk):
    """
    The mapper function: process the raw text and returns the pairs name-value.
    Args:
    - chunk(str): the raw text from data file
    Return(list of tuples): a list of 2D tuples with the pairs name-value. 
    """
    Pairs = []
    for line in chunk.split('\n'):
        data = line.strip().split(",")
        if len(data) == 6:
            zip_code, latitude, longitude, city, state, country = data
            Pairs.append((str(country), 1))
    return Pairs