def set_dependent_variable(data, dependent_variable):
    """
    Set dependent variable.
    
    This helper functions isolates the dependent variable in a data.frame.
    
    :param data: An object of class pandas.DataFrame; the data to be analyzed.
    :param dependent_variable: A string; the dependent variable for this analysis.
    :return: An ndarray, the dependent variable of the analysis.
    """
    y = data[dependent_variable].values
    return y