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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 subtract_column_median(df, prefix='Intensity '):
 """ Apply column-wise normalisation to expression columns. Default is median transform to expression columns beginning with Intensity :param df: :param prefix: The column prefix for expression columns :return: """

    df = df.copy()

    df.replace([np.inf, -np.inf], np.nan, inplace=True)

    mask = [l.startswith(prefix) for l in df.columns.values]
    df.iloc[:, mask] = df.iloc[:, mask] - df.iloc[:, mask].median(axis=0)

    return df