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.
Always greater than or equal to min_anonymity.
Sample of quasi-identifier tuple values in this bucket. The
total number of classes returned per bucket is capped at 20.
