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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 _preprocess(df):
 """ given a DataFrame where records are stored row-wise, rearrange it such that records are stored column-wise. """


    df = df.stack()

    df.index.rename(["id", "time"], inplace=True)  # .reset_index()
    df.name = "value"
    df = df.reset_index()

    return df