def extract(dataset, column_index=0):
    """
    Extracts one column from a dataset.
    :param list dataset: A list with all dataset content
    :param int column_index: The index of the column that will be extracted from dataset
    :return: A list with the column contents
    """
    column = []
    for row in dataset:
        column.append(row[column_index])
    return column