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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def pandas_dataframe_to_unit_arrays(df, column_units=None):
 """Attach units to data in pandas dataframes and return united arrays. Parameters df : `pandas.DataFrame` Data in pandas dataframe. column_units : dict Dictionary of units to attach to columns of the dataframe. Overrides the units attribute if it is attached to the dataframe. Returns ------- Dictionary containing united arrays with keys corresponding to the dataframe column names. """

    if not column_units:
        try:
            column_units = df.units
        except AttributeError:
            raise ValueError('No units attribute attached to pandas '
                             'dataframe and col_units not given.')

    # Iterate through columns attaching units if we have them, if not, don't touch it
    res = {}
    for column in df:
        if column in column_units and column_units[column]:
            res[column] = df[column].values * units(column_units[column])
        else:
            res[column] = df[column].values
    return res