Write code that finds all rows in the rate_group column of Pandas with "%" at the end and removes it with regex. Rows without "%" must be replaced with np.nan.

def remove_percent(row):
    if row.endswith("%"):
        return float(row.replace("%", ""))
    else:
        return float(row)

df.rate_group = df.rate_group.map(remove_percent)