Approximate Alternating Least Squares¶
This library supports using a couple of different approximate nearest neighbours libraries to speed up the recommend and similar_items methods of the AlternatingLeastSquares model.
The potential speedup of using these methods can be quite significant, at the risk of potentially missing relevant results:
See this post comparing the different ANN libraries for more details.
NMSLibAlternatingLeastSquares¶

class
implicit.approximate_als.
NMSLibAlternatingLeastSquares
(approximate_similar_items=True, approximate_recommend=True, method='hnsw', index_params=None, query_params=None, random_state=None, *args, **kwargs)¶ Bases:
implicit.cpu.als.AlternatingLeastSquares
Speeds up the base
AlternatingLeastSquares
model by using NMSLib to create approximate nearest neighbours indices of the latent factors.Parameters:  method (str, optional) – The NMSLib method to use
 index_params (dict, optional) – Optional params to send to the createIndex call in NMSLib
 query_params (dict, optional) – Optional query time params for the NMSLib ‘setQueryTimeParams’ call
 approximate_similar_items (bool, optional) – whether or not to build an NMSLIB index for computing similar_items
 approximate_recommend (bool, optional) – whether or not to build an NMSLIB index for the recommend call
 random_state (int, RandomState or None, optional) – The random state for seeding the initial item and user factors. Default is None.

similar_items_index
¶ NMSLib index for looking up similar items in the cosine space formed by the latent item_factors
Type: nmslib.FloatIndex

recommend_index
¶ NMSLib index for looking up similar items in the inner product space formed by the latent item_factors
Type: nmslib.FloatIndex

fit
(Ciu, show_progress=True)¶ Factorizes the item_users matrix.
After calling this method, the members ‘user_factors’ and ‘item_factors’ will be initialized with a latent factor model of the input data.
The item_users matrix does double duty here. It defines which items are liked by which users (P_iu in the original paper), as well as how much confidence we have that the user liked the item (C_iu).
The negative items are implicitly defined: This code assumes that positive items in the item_users matrix means that the user liked the item. The negatives are left unset in this sparse matrix: the library will assume that means Piu = 0 and Ciu = 1 for all these items. Negative items can also be passed with a higher confidence value by passing a negative value, indicating that the user disliked the item.
Parameters:  item_users (csr_matrix) – Matrix of confidences for the liked items. This matrix should be a csr_matrix where the rows of the matrix are the item, the columns are the users that liked that item, and the value is the confidence that the user liked the item.
 show_progress (bool, optional) – Whether to show a progress bar during fitting

recommend
(userid, user_items, N=10, filter_already_liked_items=True, filter_items=None, recalculate_user=False)¶ Recommends items for a user
Calculates the N best recommendations for a user, and returns a list of itemids, score.
Parameters:  userid (int) – The userid to calculate recommendations for
 user_items (csr_matrix) – A sparse matrix of shape (number_users, number_items). This lets us look up the liked items and their weights for the user. This is used to filter out items that have already been liked from the output, and to also potentially calculate the best items for this user.
 N (int, optional) – The number of results to return
 filter_already_liked_items (bool, optional) – When true, don’t return items present in the training set that were rated by the specificed user.
 filter_items (sequence of ints, optional) – List of extra item ids to filter out from the output
 recalculate_user (bool, optional) – When true, don’t rely on stored user state and instead recalculate from the passed in user_items
Returns: List of (itemid, score) tuples
Return type: list

similar_items
(itemid, N=10)¶ Calculates a list of similar items
Parameters:  itemid (int) – The row id of the item to retrieve similar items for
 N (int, optional) – The number of similar items to return
 react_users (csr_matrix, optional) – A sparse matrix of shape (number_items, number_users). This lets us look up the reacted users and their weights for the item.
 recalculate_item (bool, optional) – When true, don’t rely on stored item state and instead recalculate from the passed in react_users
Returns: List of (itemid, score) tuples
Return type: list
AnnoyAlternatingLeastSquares¶

class
implicit.approximate_als.
AnnoyAlternatingLeastSquares
(approximate_similar_items=True, approximate_recommend=True, n_trees=50, search_k=1, random_state=None, *args, **kwargs)¶ Bases:
implicit.cpu.als.AlternatingLeastSquares
A version of the
AlternatingLeastSquares
model that uses an Annoy index to calculate similar items and recommend items.Parameters:  n_trees (int, optional) – The number of trees to use when building the Annoy index. More trees gives higher precision when querying.
 search_k (int, optional) – Provides a way to search more trees at runtime, giving the ability to have more accurate results at the cost of taking more time.
 approximate_similar_items (bool, optional) – whether or not to build an Annoy index for computing similar_items
 approximate_recommend (bool, optional) – whether or not to build an Annoy index for the recommend call
 random_state (int, RandomState or None, optional) – The random state for seeding the initial item and user factors. Default is None.

similar_items_index
¶ Annoy index for looking up similar items in the cosine space formed by the latent item_factors
Type: annoy.AnnoyIndex

recommend_index
¶ Annoy index for looking up similar items in the inner product space formed by the latent item_factors
Type: annoy.AnnoyIndex

fit
(Ciu, show_progress=True)¶ Factorizes the item_users matrix.
After calling this method, the members ‘user_factors’ and ‘item_factors’ will be initialized with a latent factor model of the input data.
The item_users matrix does double duty here. It defines which items are liked by which users (P_iu in the original paper), as well as how much confidence we have that the user liked the item (C_iu).
The negative items are implicitly defined: This code assumes that positive items in the item_users matrix means that the user liked the item. The negatives are left unset in this sparse matrix: the library will assume that means Piu = 0 and Ciu = 1 for all these items. Negative items can also be passed with a higher confidence value by passing a negative value, indicating that the user disliked the item.
Parameters:  item_users (csr_matrix) – Matrix of confidences for the liked items. This matrix should be a csr_matrix where the rows of the matrix are the item, the columns are the users that liked that item, and the value is the confidence that the user liked the item.
 show_progress (bool, optional) – Whether to show a progress bar during fitting

recommend
(userid, user_items, N=10, filter_already_liked_items=True, filter_items=None, recalculate_user=False)¶ Recommends items for a user
Calculates the N best recommendations for a user, and returns a list of itemids, score.
Parameters:  userid (int) – The userid to calculate recommendations for
 user_items (csr_matrix) – A sparse matrix of shape (number_users, number_items). This lets us look up the liked items and their weights for the user. This is used to filter out items that have already been liked from the output, and to also potentially calculate the best items for this user.
 N (int, optional) – The number of results to return
 filter_already_liked_items (bool, optional) – When true, don’t return items present in the training set that were rated by the specificed user.
 filter_items (sequence of ints, optional) – List of extra item ids to filter out from the output
 recalculate_user (bool, optional) – When true, don’t rely on stored user state and instead recalculate from the passed in user_items
Returns: List of (itemid, score) tuples
Return type: list

similar_items
(itemid, N=10)¶ Calculates a list of similar items
Parameters:  itemid (int) – The row id of the item to retrieve similar items for
 N (int, optional) – The number of similar items to return
 react_users (csr_matrix, optional) – A sparse matrix of shape (number_items, number_users). This lets us look up the reacted users and their weights for the item.
 recalculate_item (bool, optional) – When true, don’t rely on stored item state and instead recalculate from the passed in react_users
Returns: List of (itemid, score) tuples
Return type: list
FaissAlternatingLeastSquares¶

class
implicit.approximate_als.
FaissAlternatingLeastSquares
(approximate_similar_items=True, approximate_recommend=True, nlist=400, nprobe=20, use_gpu=False, random_state=None, *args, **kwargs)¶ Bases:
implicit.cpu.als.AlternatingLeastSquares
Speeds up the base
AlternatingLeastSquares
model by using Faiss to create approximate nearest neighbours indices of the latent factors.Parameters:  nlist (int, optional) – The number of cells to use when building the Faiss index.
 nprobe (int, optional) – The number of cells to visit to perform a search.
 use_gpu (bool, optional) – Whether or not to enable run Faiss on the GPU. Requires faiss to have been built with GPU support.
 approximate_similar_items (bool, optional) – whether or not to build an Faiss index for computing similar_items
 approximate_recommend (bool, optional) – whether or not to build an Faiss index for the recommend call
 random_state (int, RandomState or None, optional) – The random state for seeding the initial item and user factors. Default is None.

similar_items_index
¶ Faiss index for looking up similar items in the cosine space formed by the latent item_factors
Type: faiss.IndexIVFFlat

recommend_index
¶ Faiss index for looking up similar items in the inner product space formed by the latent item_factors
Type: faiss.IndexIVFFlat

fit
(Ciu, show_progress=True)¶ Factorizes the item_users matrix.
After calling this method, the members ‘user_factors’ and ‘item_factors’ will be initialized with a latent factor model of the input data.
The item_users matrix does double duty here. It defines which items are liked by which users (P_iu in the original paper), as well as how much confidence we have that the user liked the item (C_iu).
The negative items are implicitly defined: This code assumes that positive items in the item_users matrix means that the user liked the item. The negatives are left unset in this sparse matrix: the library will assume that means Piu = 0 and Ciu = 1 for all these items. Negative items can also be passed with a higher confidence value by passing a negative value, indicating that the user disliked the item.
Parameters:  item_users (csr_matrix) – Matrix of confidences for the liked items. This matrix should be a csr_matrix where the rows of the matrix are the item, the columns are the users that liked that item, and the value is the confidence that the user liked the item.
 show_progress (bool, optional) – Whether to show a progress bar during fitting

recommend
(userid, user_items, N=10, filter_already_liked_items=True, filter_items=None, recalculate_user=False)¶ Recommends items for a user
Calculates the N best recommendations for a user, and returns a list of itemids, score.
Parameters:  userid (int) – The userid to calculate recommendations for
 user_items (csr_matrix) – A sparse matrix of shape (number_users, number_items). This lets us look up the liked items and their weights for the user. This is used to filter out items that have already been liked from the output, and to also potentially calculate the best items for this user.
 N (int, optional) – The number of results to return
 filter_already_liked_items (bool, optional) – When true, don’t return items present in the training set that were rated by the specificed user.
 filter_items (sequence of ints, optional) – List of extra item ids to filter out from the output
 recalculate_user (bool, optional) – When true, don’t rely on stored user state and instead recalculate from the passed in user_items
Returns: List of (itemid, score) tuples
Return type: list

similar_items
(itemid, N=10)¶ Calculates a list of similar items
Parameters:  itemid (int) – The row id of the item to retrieve similar items for
 N (int, optional) – The number of similar items to return
 react_users (csr_matrix, optional) – A sparse matrix of shape (number_items, number_users). This lets us look up the reacted users and their weights for the item.
 recalculate_item (bool, optional) – When true, don’t rely on stored item state and instead recalculate from the passed in react_users
Returns: List of (itemid, score) tuples
Return type: list