<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def getContGroupArrays(arrays, groupPositions, arrayKeys=None):
 """Convinience function to generate a subset of arrays from specified array positions. :param arrays: a dictionary containing ``numpy.arrays`` :param groupPositions: arrays positions that should be included in the subset of arrays :param arrayKeys: a list of "arrays" keys that should be included in the subset of arrays, if None all keys are selected :returns: a dictionary containing ``numpy.arrays`` """

    if arrayKeys is None:
        arrayKeys = list(viewkeys(arrays))
    matchingArrays = dict()
    for key in arrayKeys:
        matchingArrays[key] = arrays[key][groupPositions]
    return matchingArrays