Package it.unimi.dsi.util

Class FrontCodedStringList

java.lang.Object

java.util.AbstractCollection<K>

it.unimi.dsi.fastutil.objects.AbstractObjectCollection<K>

it.unimi.dsi.fastutil.objects.AbstractObjectList<MutableString>

it.unimi.dsi.util.FrontCodedStringList

All Implemented Interfaces:

ObjectCollection<MutableString>, ObjectIterable<MutableString>, ObjectList<MutableString>, Stack<MutableString>, Serializable, Comparable<List<? extends MutableString>>, Iterable<MutableString>, Collection<MutableString>, List<MutableString>, RandomAccess

public class FrontCodedStringList
extends AbstractObjectList<MutableString>
implements RandomAccess, Serializable

Compact storage of strings using front-coding compression (also known as compression by prefix omission).

This class stores a list of strings using front-coding (also known as prefix-omission) compression; the compression will be reasonable only if the list is sorted, but you could also use instances of this class just as a handy way to manage a large amount of strings. It implements an immutable ObjectList that returns the i-th string (as a MutableString) when the get(int) method is called with argument i. The returned mutable string may be freely modified.

As a commodity, this class provides a main method that reads from standard input a sequence of newline-separated strings, and writes a corresponding serialized front-coded string list.

Implementation Details

To store the list of strings, we use either a UTF-8 coded ByteArrayFrontCodedList, or a CharArrayFrontCodedList, depending on the value of the utf8 parameter at creation time. In the first case, if the strings are ASCII-oriented the resulting array will be much smaller, but access times will increase manifold, as each string must be UTF-8 decoded before being returned.

See Also:

• Serialized Form

Nested Class Summary

Nested classes/interfaces inherited from class it.unimi.dsi.fastutil.objects.AbstractObjectList

AbstractObjectList.ObjectRandomAccessSubList<K extends Object>, AbstractObjectList.ObjectSubList<K extends Object>

Field Summary

Fields

Modifier and Type	Field	Description
protected final ByteArrayFrontCodedList	byteFrontCodedList	The underlying ByteArrayFrontCodedList, or null.
protected final CharArrayFrontCodedList	charFrontCodedList	The underlying CharArrayFrontCodedList, or null.
static final long	serialVersionUID
protected final boolean	utf8	Whether this front-coded list is UTF-8 encoded.

Constructor Summary

Constructors

Constructor	Description
FrontCodedStringList(Collection<? extends CharSequence> c, int ratio, boolean utf8)	Creates a new front-coded string list containing the character sequences contained in the given collection.
FrontCodedStringList(Iterator<? extends CharSequence> words, int ratio, boolean utf8)	Creates a new front-coded string list containing the character sequences returned by the given iterator.

Method Summary

Modifier and Type	Method	Description
protected static char[]	byte2Char(byte[] a, char[] s)
protected static int	countUTF8Chars(byte[] a)
MutableString	get(int index)	Returns the element at the specified position in this front-coded string list as a mutable string.
void	get(int index, MutableString s)	Returns the element at the specified position in this front-coded string list by storing it in a mutable string.
ObjectListIterator<MutableString>	listIterator(int k)
static void	main(String[] arg)
int	ratio()	Returns the ratio of the underlying front-coded list.
int	size()
boolean	utf8()	Returns whether this front-coded string list is storing its strings as UTF-8 encoded bytes.

Methods inherited from class it.unimi.dsi.fastutil.objects.AbstractObjectList

add, add, addAll, addAll, addElements, addElements, clear, compareTo, contains, ensureIndex, ensureRestrictedIndex, equals, forEach, getElements, hashCode, indexOf, iterator, lastIndexOf, listIterator, peek, pop, push, remove, removeElements, set, setElements, size, subList, toArray, toArray, top, toString

Methods inherited from class java.util.AbstractCollection

containsAll, isEmpty, remove, removeAll, retainAll

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Methods inherited from interface java.util.Collection

parallelStream, removeIf, stream, toArray

Methods inherited from interface java.util.List

containsAll, isEmpty, remove, removeAll, replaceAll, retainAll

Methods inherited from interface it.unimi.dsi.fastutil.objects.ObjectCollection

spliterator

Methods inherited from interface it.unimi.dsi.fastutil.objects.ObjectList

addAll, addAll, setElements, setElements, sort, spliterator, unstableSort

Methods inherited from interface it.unimi.dsi.fastutil.Stack

isEmpty

Field Details

serialVersionUID

public static final long serialVersionUID

See Also:

• Constant Field Values

byteFrontCodedList

protected final ByteArrayFrontCodedList byteFrontCodedList

The underlying ByteArrayFrontCodedList, or null.

charFrontCodedList

protected final CharArrayFrontCodedList charFrontCodedList

The underlying CharArrayFrontCodedList, or null.

utf8

protected final boolean utf8

Whether this front-coded list is UTF-8 encoded.

Constructor Details

FrontCodedStringList

public FrontCodedStringList(Iterator<? extends CharSequence> words,
 int ratio,
 boolean utf8)

Creates a new front-coded string list containing the character sequences returned by the given iterator.

Parameters:

words - an iterator returning character sequences.

ratio - the desired ratio.

utf8 - if true, the strings will be stored as UTF-8 byte arrays.

FrontCodedStringList

public FrontCodedStringList(Collection<? extends CharSequence> c,
 int ratio,
 boolean utf8)

Creates a new front-coded string list containing the character sequences contained in the given collection.

Parameters:

c - a collection containing character sequences.

ratio - the desired ratio.

utf8 - if true, the strings will be stored as UTF-8 byte arrays.

Method Details

utf8

public boolean utf8()

Returns whether this front-coded string list is storing its strings as UTF-8 encoded bytes.

Returns:

true if this front-coded string list is keeping its data as an array of UTF-8 encoded bytes.

ratio

public int ratio()

Returns the ratio of the underlying front-coded list.

Returns:

the ratio of the underlying front-coded list.

get

public MutableString get(int index)

Returns the element at the specified position in this front-coded string list as a mutable string.

Specified by:

get in interface List<MutableString>

Parameters:

index - an index in the list.

Returns:

a MutableString that will contain the string at the specified position. The string may be freely modified.

get

public void get(int index,
 MutableString s)

Returns the element at the specified position in this front-coded string list by storing it in a mutable string.

Parameters:

index - an index in the list.

s - a mutable string that will contain the string at the specified position.

countUTF8Chars

protected static int countUTF8Chars(byte[] a)

byte2Char

protected static char[] byte2Char(byte[] a,
 char[] s)

listIterator

public ObjectListIterator<MutableString> listIterator(int k)

Specified by:

listIterator in interface List<MutableString>

Specified by:

listIterator in interface ObjectList<MutableString>

Overrides:

listIterator in class AbstractObjectList<MutableString>

size

public int size()

Specified by:

size in interface Collection<MutableString>

Specified by:

size in interface List<MutableString>

Specified by:

size in class AbstractCollection<MutableString>

main

public static void main(String[] arg)
                 throws IOException,
JSAPException,
NoSuchMethodException

Throws:

IOException

JSAPException

NoSuchMethodException