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| <div class="block">The hllmap package contains a space efficient HLL mapping sketch of keys to approximate unique |
| count of identifiers. For example, counting the number of unique users (identifiers) per IP |
| address. |
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| <p>In cases where the number of keys is very large, having an individual HLL sketch per key may |
| not be practical. If the distribution of values per key is highly skewed where the vast |
| majority of keys have only a few values then this mapping sketch will make sense as it will be |
| far more space efficient than dedicating individual HLL sketches per key. |
| |
| <p>From our own testing, sketching 100 million IPv4 addresses with such a |
| highly skewed distribution of identifiers per IP uses only 1.4GB of memory. This translates to |
| an average of about 10 bytes per IP allocated to the equivalent of a full k=1024 HLL sketch |
| and provides an RSE of less than 2.5%. Your results will vary depending on the actual |
| distribution of identifiers per key.</div> |
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| <dd><a href="UniqueCountMap.html" title="class in org.apache.datasketches.hllmap"><code>UniqueCountMap</code></a></dd> |
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| <div class="block">This is a real-time, key-value HLL mapping sketch that tracks approximate unique counts of |
| identifiers (the values) associated with each key.</div> |
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