it.unimi.dsi.sux4j.mph
Class HollowTrieDistributor<T>
java.lang.Object
it.unimi.dsi.fastutil.objects.AbstractObject2LongFunction<T>
it.unimi.dsi.sux4j.mph.HollowTrieDistributor<T>
- All Implemented Interfaces:
- Function<T,Long>, Object2LongFunction<T>, Serializable
public class HollowTrieDistributor<T>
- extends AbstractObject2LongFunction<T>
A distributor based on a hollow trie.
Implementation details
This class implements a distributor on top of a hollow trie. First, a compacted trie is built from the delimiter set.
Then, for each key we compute the node of the trie in which the bucket of the key is established. This gives us,
for each node of the trie, a set of paths to which we must associate an action (exit on the left,
go through, exit on the right). Overall, the number of such paths is equal to the number of keys plus the number of delimiters, so
the mapping from each pair node/path to the respective action takes linear space. Now, from the compacted trie we just
retain a hollow trie, as the path-length information is sufficient to rebuild the keys of the above mapping.
By sizing the bucket size around the logarithm of the average length, we obtain a distributor that occupies linear space.
- See Also:
- Serialized Form
Field Summary |
protected double |
meanSkipLength
The average skip length in bits (actually, the average length in bits of a skip length increased by one). |
Methods inherited from class java.lang.Object |
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait |
meanSkipLength
protected double meanSkipLength
- The average skip length in bits (actually, the average length in bits of a skip length increased by one).
HollowTrieDistributor
public HollowTrieDistributor(Iterable<? extends T> elements,
int log2BucketSize,
TransformationStrategy<? super T> transformationStrategy)
throws IOException
- Creates a partial compacted trie using given elements, bucket size and transformation strategy.
- Parameters:
elements
- the elements among which the trie must be able to rank.log2BucketSize
- the logarithm of the size of a bucket.transformationStrategy
- a transformation strategy that must turn the elements in elements
into a list of
distinct, lexicographically increasing (in iteration order) bit vectors.
- Throws:
IOException
HollowTrieDistributor
public HollowTrieDistributor(Iterable<? extends T> elements,
int log2BucketSize,
TransformationStrategy<? super T> transformationStrategy,
File tempDir)
throws IOException
- Creates a hollow trie distributor.
- Parameters:
elements
- the elements among which the trie must be able to rank.log2BucketSize
- the logarithm of the size of a bucket.transformationStrategy
- a transformation strategy that must turn the elements in elements
into a list of
distinct, lexicographically increasing (in iteration order) bit vectors.tempDir
- the directory where temporary files will be created, or for the default directory
.
- Throws:
IOException
getLong
public long getLong(Object o)
numBits
public long numBits()
containsKey
public boolean containsKey(Object o)
size
public int size()
bitsPerSkip
public double bitsPerSkip()