Avoid SettingWithCopyWarning in ARM5_4 example

These changes fix the following warning from Pandas
(v0.13.1-63-gcc6ee40).

    pandas/core/generic.py:1826: SettingWithCopyWarning:

    A value is trying to be set on a copy of a slice from a DataFrame.
    Try using .loc[row_index,col_indexer] = value instead self[name] =
    value