Libraries in Use
LensKit makes use of several libraries throughout its design. While primary public recommender APIs do not mandate use of these libraries, you will encounter them when you write your own recommender components and algorithms.
Fastutil
We use the fastutil library for optimized primitive collections, such as lists of long
or double
values and maps of the same. One of the most common types is Long2DoubleMap
, which we use to represent sparse vectors mapping user or item IDs to values.
The LensKit utility class Vectors provides utilities for performing vector computations on vectors represented by Long2DoubleMap
, such as dot products and Euclidean norms.
We also provide highly memoryefficient, immutable implementations of LongSortedSet
and Long2DoubleSortedMap
accessible through the LongUtils utility class (see the frozenSet
and frozenMap
methods). These implementations use sorted arrays to provide \(O(\mathrm{lg}\ n)\) lookup and Vectors
methods take advantage of their layout to provide lineartime pairwise operations such as dot products. They also do not have excess overhead due to unused space, unlike the hashtable implementations of maps and sets. Further, when none of the long
values exceed the storage space of an int
, these implementations will use int
arrays instead of long
arrays to further reduce memory consumption.
It is a common pattern to use a Long2DoubleOpenHashMap
to accumulate results and then convert them to an optimized map using LongUtils.frozenMap
for longerterm storage.
Guava
We use Google Guava library extensively in LensKit. A number of LensKit classes make use of its Predicate
and Function
interfaces, and we use its collection and I/O utilities quite a bit.
Grapht
We use the Grapht dependency injection container to configure and instantiate LensKit recommender components. If you have used Google Guice, many aspects of Grapht should be familiar.
Commons Math 3
We use Apache Commons Math for linear algebra, including dense vectors and matrices.
Other Libraries
There are several other libraries we use in LensKit, including:

Commons Lang

SLF4J

JodaConvert