TypeError: 'GroupedData' object is not iterable in pyspark

[#1]

I'm using pyspark 2.0.1 & python 2.7.I'm running following code & getting error message as

TypeError: 'GroupedData' object is not iterable in pyspark.Can you pleas help me?

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# This will return a new DF with all the columns + iddata1 = data.withColumn("id", monotonically_increasing_id()) # Create an integer indexdata1.show()

def create_indexes(df,                   fields=['country', 'state_id', 'airport', 'airport_id']):
    """ Create indexes for the different element ids
        for CMRs. This allows us to select CMRs that match
        a given element and element value very quickly.
    """
    if fields == None:
        print("No fields specified, returning")
        return
    for field in fields:
        if field not in df.columns:
            print('field: ', field, " is not in the data...")
            return    indexes = {}
    for field in fields:
        print(field)        res = df.groupby(field)        index = {label: np.array(vals['id'], np.int32) for label, vals in res}        indexes[field] = index
    return indexes

# Create indexes. Some of them take a lot of time!
#Changed dom_client_id by gbl_buy_grp_id as it was changed in Line Number indexes = create_indexes(data1, fields=['country', 'state_id', 'airport', 'airport_id'])
print type(indexes)

[#2]

Any help please?