A KMapEstimationHistogramBucket message with the following values:
min_anonymity: 3 max_anonymity: 5 frequency: 42 means that there are
42 records whose quasi-identifier values correspond to 3, 4 or 5
people in the overlying population. An important particular case is
when min_anonymity = max_anonymity = 1: the frequency field then
corresponds to the number of uniquely identifiable records.
.. attribute:: min_anonymity
Always positive.
Number of records within these anonymity bounds.
Total number of distinct quasi-identifier tuple values in this
bucket.
