org.grouplens.lenskit.cursors

Class Cursors

java.lang.Object

org.grouplens.lenskit.cursors.Cursors

public final class Cursors
extends Object

Utility methods for cursors.

Author:

GroupLens Research

Compatibility: Public

Method Summary

Methods

Modifier and Type	Method and Description
static <T> Cursor<T>	empty() Create an empty cursor.
static <T> Cursor<T>	filter(Cursor<?> cursor, Class<T> type) Filter a cursor to only contain elements of type type.
static <T> Cursor<T>	filter(Cursor<T> cursor, Predicate<? super T> predicate) Filter a cursor.
static <T> ArrayList<T>	makeList(Cursor<? extends T> cursor) Read a cursor into a list, closing when it is finished.
static LongArrayList	makeList(LongCursor cursor) Read a LongCursor into a LongArrayList, closing the cursor when done.
static LongCursor	makeLongCursor(Cursor<Long> cursor) Make a fast long cursor.
static LongSet	makeSet(LongCursor cursor) Read a LongCursor into a LongSet, closing the cursor when done.
static <T> Cursor<T>	sort(Cursor<T> cursor, Comparator<? super T> comp) Sort a cursor.
static <S,T> Cursor<T>	transform(Cursor<S> cursor, Function<? super S,? extends T> function) Transform a cursor's values.
static <T> Cursor<T>	wrap(Collection<? extends T> collection) Wrap a collection in a cursor.
static <T> Cursor<T>	wrap(Iterator<? extends T> iterator) Wrap an iterator in a cursor.
static LongCursor	wrap(LongCollection collection) Construct a cursor over a collection.
static LongCursor	wrap(LongIterator iter) Wrap a long iterator in a cursor.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Detail

wrap

public static <T> Cursor<T> wrap(Iterator<? extends T> iterator)

Wrap an iterator in a cursor.

Type Parameters:

T - The type of data to return.

Parameters:

iterator - An iterator to wrap

Returns:

A cursor returning the elements of the iterator.

wrap

public static <T> Cursor<T> wrap(Collection<? extends T> collection)

Wrap a collection in a cursor.

Type Parameters:

T - The type of data to return.

Parameters:

collection - A collection to wrap

Returns:

A cursor returning the elements of the collection.

filter

public static <T> Cursor<T> filter(@WillCloseWhenClosed
                   Cursor<T> cursor,
                   Predicate<? super T> predicate)

Filter a cursor.

Type Parameters:

T - The type of cursor rows.

Parameters:

cursor - The source cursor.

predicate - A predicate indicating which rows to return.

Returns:

A cursor returning all rows for which predicate returns true.

filter

public static <T> Cursor<T> filter(@WillCloseWhenClosed
                   Cursor<?> cursor,
                   Class<T> type)

Filter a cursor to only contain elements of type type. Unlike filter(Cursor, Predicate) with a predicate from Predicates.instanceOf(Class), this method also transforms the cursor to be of the target type.

Type Parameters:

T - The type of value in the cursor.

Parameters:

cursor - The source cursor.

type - The type to filter.

Returns:

A cursor returning all elements in cursor which are instances of type type.

transform

public static <S,T> Cursor<T> transform(@WillCloseWhenClosed
                        Cursor<S> cursor,
                        Function<? super S,? extends T> function)

Transform a cursor's values.

Type Parameters:

S - The type of source cursor rows

T - The type of output cursor rows

Parameters:

cursor - The source cursor

function - A function to apply to each row in the cursor.

Returns:

A new cursor iterating the results of function.

empty

public static <T> Cursor<T> empty()

Create an empty cursor.

Type Parameters:

T - The type of value in the cursor.

Returns:

An empty cursor.

makeList

public static <T> ArrayList<T> makeList(@WillClose
                        Cursor<? extends T> cursor)

Read a cursor into a list, closing when it is finished.

Type Parameters:

T - The type of item in the cursor.

Parameters:

cursor - The cursor.

Returns:

A new list containing the elements of the cursor. The list has been allocated with a capacity of Cursor.getRowCount() if possible, but has not been trimmed.

makeList

public static LongArrayList makeList(@WillClose
                     LongCursor cursor)

Read a LongCursor into a LongArrayList, closing the cursor when done.

Parameters:

cursor - The LongCursor to be read into a list.

Returns:

A new list containing the elements of the cursor. The list has been allocated with a capacity of Cursor.getRowCount() if possible, but has not been trimmed.

makeSet

public static LongSet makeSet(@WillClose
              LongCursor cursor)

Read a LongCursor into a LongSet, closing the cursor when done.

Parameters:

cursor - The LongCursor to be read into a set.

Returns:

A LongSet containing the elements of the cursor.

wrap

public static LongCursor wrap(LongIterator iter)

Wrap a long iterator in a cursor.

Parameters:

iter - An iterator.

Returns:

A cursor backed by iter. Closing the cursor is a no-op.

wrap

public static LongCursor wrap(LongCollection collection)

Construct a cursor over a collection.

Parameters:

collection - A collection.

Returns:

A cursor over the collection. Closing the cursor is a no-op.

makeLongCursor

public static LongCursor makeLongCursor(@WillCloseWhenClosed
                        Cursor<Long> cursor)

Make a fast long cursor.

Parameters:

cursor - A cursor.

Returns:

A LongCursor. If cursor is a LongCursor, it is returned.

sort

public static <T> Cursor<T> sort(@WillClose
                 Cursor<T> cursor,
                 Comparator<? super T> comp)

Sort a cursor. This reads the original cursor into a list, sorts it, and returns a new cursor backed by the list (after closing the original cursor).

Type Parameters:

T - The type of value in the cursor.

Parameters:

cursor - The cursor to sort.

comp - The comparator to use to sort the cursor.

Returns:

A cursor iterating over the sorted results.