Link prediction

Link prediction algorithms.

The method predict assigns a scores to edges.

First order methods

class sknetwork.linkpred.CommonNeighbors

Link prediction by common neighbors:

\(s(i, j) = |\Gamma_i \cap \Gamma_j|\).

Variables

• indptr_ (np.ndarray) – Pointer index for neighbors.

• indices_ (np.ndarray) – Concatenation of neighbors.

Examples

>>> from sknetwork.data import house
>>> adjacency = house()
>>> cn = CommonNeighbors()
>>> similarities = cn.fit_predict(adjacency, 0)
>>> similarities
array([2, 1, 1, 1, 1])
>>> similarities = cn.predict([0, 1])
>>> similarities
array([[2, 1, 1, 1, 1],
       [1, 3, 0, 2, 1]])
>>> similarities = cn.predict((0, 1))
>>> similarities
1
>>> similarities = cn.predict([(0, 1), (1, 2)])
>>> similarities
array([1, 0])

fit(adjacency: Union[scipy.sparse.csr.csr_matrix, numpy.ndarray])

Fit algorithm to the data.

Parameters

adjacency – Adjacency matrix of the graph

Returns

self

Return type

FirstOrder

fit_predict(adjacency, query)

Fit algorithm to data and compute scores for requested edges.

predict(query: Union[int, Iterable, Tuple])

Compute similarity scores.

Parameters

query (int, list, array or Tuple) –

• If int i, return the similarities s(i, j) for all j.

• If list or array integers, return s(i, j) for i in query, for all j as array.

• If tuple (i, j), return the similarity s(i, j).

• If list of tuples or array of shape (n_queries, 2), return s(i, j) for (i, j) in query as array.

Returns

predictions – The prediction scores.

Return type

int, float or array

class sknetwork.linkpred.JaccardIndex

Link prediction by Jaccard Index:

\(s(i, j) = \dfrac{|\Gamma_i \cap \Gamma_j|}{|\Gamma_i \cup \Gamma_j|}\).

Variables

• indptr_ (np.ndarray) – Pointer index for neighbors.

• indices_ (np.ndarray) – Concatenation of neighbors.

Examples

>>> from sknetwork.data import house
>>> adjacency = house()
>>> jaccard = JaccardIndex()
>>> similarities = jaccard.fit_predict(adjacency, 0)
>>> similarities.round(2)
array([1.  , 0.25, 0.33, 0.33, 0.25])
>>> similarities = jaccard.predict([0, 1])
>>> similarities.round(2)
array([[1.  , 0.25, 0.33, 0.33, 0.25],
       [0.25, 1.  , 0.  , 0.67, 0.2 ]])
>>> similarities = jaccard.predict((0, 1))
>>> similarities.round(2)
0.25
>>> similarities = jaccard.predict([(0, 1), (1, 2)])
>>> similarities.round(2)
array([0.25, 0.  ])

References

Levandowsky, M., & Winter, D. (1971). Distance between sets. Nature, 234(5323), 34-35.

fit(adjacency: Union[scipy.sparse.csr.csr_matrix, numpy.ndarray])

Fit algorithm to the data.

Parameters

adjacency – Adjacency matrix of the graph

Returns

self

Return type

FirstOrder

fit_predict(adjacency, query)

Fit algorithm to data and compute scores for requested edges.

predict(query: Union[int, Iterable, Tuple])

Compute similarity scores.

Parameters

query (int, list, array or Tuple) –

• If int i, return the similarities s(i, j) for all j.

• If list or array integers, return s(i, j) for i in query, for all j as array.

• If tuple (i, j), return the similarity s(i, j).

• If list of tuples or array of shape (n_queries, 2), return s(i, j) for (i, j) in query as array.

Returns

predictions – The prediction scores.

Return type

int, float or array

class sknetwork.linkpred.SaltonIndex

Link prediction by Salton Index:

\(s(i, j) = \dfrac{|\Gamma_i \cap \Gamma_j|}{\sqrt{|\Gamma_i|.|\Gamma_j|}}\).

Variables

• indptr_ (np.ndarray) – Pointer index for neighbors.

• indices_ (np.ndarray) – Concatenation of neighbors.

Examples

>>> from sknetwork.data import house
>>> adjacency = house()
>>> salton = SaltonIndex()
>>> similarities = salton.fit_predict(adjacency, 0)
>>> similarities.round(2)
array([1.  , 0.41, 0.5 , 0.5 , 0.41])
>>> similarities = salton.predict([0, 1])
>>> similarities.round(2)
array([[1.  , 0.41, 0.5 , 0.5 , 0.41],
       [0.41, 1.  , 0.  , 0.82, 0.33]])
>>> similarities = salton.predict((0, 1))
>>> similarities.round(2)
0.41
>>> similarities = salton.predict([(0, 1), (1, 2)])
>>> similarities.round(2)
array([0.41, 0.  ])

References

Martínez, V., Berzal, F., & Cubero, J. C. (2016). A survey of link prediction in complex networks. ACM computing surveys (CSUR), 49(4), 1-33.

fit(adjacency: Union[scipy.sparse.csr.csr_matrix, numpy.ndarray])

Fit algorithm to the data.

Parameters

adjacency – Adjacency matrix of the graph

Returns

self

Return type

FirstOrder

fit_predict(adjacency, query)

Fit algorithm to data and compute scores for requested edges.

predict(query: Union[int, Iterable, Tuple])

Compute similarity scores.

Parameters

query (int, list, array or Tuple) –

• If int i, return the similarities s(i, j) for all j.

• If list or array integers, return s(i, j) for i in query, for all j as array.

• If tuple (i, j), return the similarity s(i, j).

• If list of tuples or array of shape (n_queries, 2), return s(i, j) for (i, j) in query as array.

Returns

predictions – The prediction scores.

Return type

int, float or array

class sknetwork.linkpred.SorensenIndex

Link prediction by Salton Index:

\(s(i, j) = \dfrac{2|\Gamma_i \cap \Gamma_j|}{|\Gamma_i|+|\Gamma_j|}\).

Variables

• indptr_ (np.ndarray) – Pointer index for neighbors.

• indices_ (np.ndarray) – Concatenation of neighbors.

Examples

>>> from sknetwork.data import house
>>> adjacency = house()
>>> sorensen = SorensenIndex()
>>> similarities = sorensen.fit_predict(adjacency, 0)
>>> similarities.round(2)
array([1. , 0.4, 0.5, 0.5, 0.4])
>>> similarities = sorensen.predict([0, 1])
>>> similarities.round(2)
array([[1.  , 0.4 , 0.5 , 0.5 , 0.4 ],
       [0.4 , 1.  , 0.  , 0.8 , 0.33]])
>>> similarities = sorensen.predict((0, 1))
>>> similarities.round(2)
0.4
>>> similarities = sorensen.predict([(0, 1), (1, 2)])
>>> similarities.round(2)
array([0.4, 0. ])

References

• Sørensen, T. J. (1948). A method of establishing groups of equal amplitude in plant sociology based on similarity of species content and its application to analyses of the vegetation on Danish commons. I kommission hos E. Munksgaard.

• Martínez, V., Berzal, F., & Cubero, J. C. (2016). A survey of link prediction in complex networks. ACM computing surveys (CSUR), 49(4), 1-33.

fit(adjacency: Union[scipy.sparse.csr.csr_matrix, numpy.ndarray])

Fit algorithm to the data.

Parameters

adjacency – Adjacency matrix of the graph

Returns

self

Return type

FirstOrder

fit_predict(adjacency, query)

Fit algorithm to data and compute scores for requested edges.

predict(query: Union[int, Iterable, Tuple])

Compute similarity scores.

Parameters

query (int, list, array or Tuple) –

• If int i, return the similarities s(i, j) for all j.

• If list or array integers, return s(i, j) for i in query, for all j as array.

• If tuple (i, j), return the similarity s(i, j).

• If list of tuples or array of shape (n_queries, 2), return s(i, j) for (i, j) in query as array.

Returns

predictions – The prediction scores.

Return type

int, float or array

class sknetwork.linkpred.HubPromotedIndex

Link prediction by Hub Promoted Index:

\(s(i, j) = \dfrac{2|\Gamma_i \cap \Gamma_j|}{min(|\Gamma_i|,|\Gamma_j|)}\).

Variables

• indptr_ (np.ndarray) – Pointer index for neighbors.

• indices_ (np.ndarray) – Concatenation of neighbors.

Examples

>>> from sknetwork.data import house
>>> adjacency = house()
>>> hpi = HubPromotedIndex()
>>> similarities = hpi.fit_predict(adjacency, 0)
>>> similarities.round(2)
array([1. , 0.5, 0.5, 0.5, 0.5])
>>> similarities = hpi.predict([0, 1])
>>> similarities.round(2)
array([[1.  , 0.5 , 0.5 , 0.5 , 0.5 ],
       [0.5 , 1.  , 0.  , 1.  , 0.33]])
>>> similarities = hpi.predict((0, 1))
>>> similarities.round(2)
0.5
>>> similarities = hpi.predict([(0, 1), (1, 2)])
>>> similarities.round(2)
array([0.5, 0. ])

References

Ravasz, E., Somera, A. L., Mongru, D. A., Oltvai, Z. N., & Barabási, A. L. (2002). Hierarchical organization of modularity in metabolic networks. science, 297(5586), 1551-1555.

fit(adjacency: Union[scipy.sparse.csr.csr_matrix, numpy.ndarray])

Fit algorithm to the data.

Parameters

adjacency – Adjacency matrix of the graph

Returns

self

Return type

FirstOrder

fit_predict(adjacency, query)

Fit algorithm to data and compute scores for requested edges.

predict(query: Union[int, Iterable, Tuple])

Compute similarity scores.

Parameters

query (int, list, array or Tuple) –

• If int i, return the similarities s(i, j) for all j.

• If list or array integers, return s(i, j) for i in query, for all j as array.

• If tuple (i, j), return the similarity s(i, j).

• If list of tuples or array of shape (n_queries, 2), return s(i, j) for (i, j) in query as array.

Returns

predictions – The prediction scores.

Return type

int, float or array

class sknetwork.linkpred.HubDepressedIndex

Link prediction by Hub Depressed Index:

\(s(i, j) = \dfrac{2|\Gamma_i \cap \Gamma_j|}{max(|\Gamma_i|,|\Gamma_j|)}\).

Variables

• indptr_ (np.ndarray) – Pointer index for neighbors.

• indices_ (np.ndarray) – Concatenation of neighbors.

Examples

>>> from sknetwork.data import house
>>> adjacency = house()
>>> hdi = HubDepressedIndex()
>>> similarities = hdi.fit_predict(adjacency, 0)
>>> similarities.round(2)
array([1.  , 0.33, 0.5 , 0.5 , 0.33])
>>> similarities = hdi.predict([0, 1])
>>> similarities.round(2)
array([[1.  , 0.33, 0.5 , 0.5 , 0.33],
       [0.33, 1.  , 0.  , 0.67, 0.33]])
>>> similarities = hdi.predict((0, 1))
>>> similarities.round(2)
0.33
>>> similarities = hdi.predict([(0, 1), (1, 2)])
>>> similarities.round(2)
array([0.33, 0.  ])

References

Ravasz, E., Somera, A. L., Mongru, D. A., Oltvai, Z. N., & Barabási, A. L. (2002). Hierarchical organization of modularity in metabolic networks. science, 297(5586), 1551-1555.

fit(adjacency: Union[scipy.sparse.csr.csr_matrix, numpy.ndarray])

Fit algorithm to the data.

Parameters

adjacency – Adjacency matrix of the graph

Returns

self

Return type

FirstOrder

fit_predict(adjacency, query)

Fit algorithm to data and compute scores for requested edges.

predict(query: Union[int, Iterable, Tuple])

Compute similarity scores.

Parameters

query (int, list, array or Tuple) –

• If int i, return the similarities s(i, j) for all j.

• If list or array integers, return s(i, j) for i in query, for all j as array.

• If tuple (i, j), return the similarity s(i, j).

• If list of tuples or array of shape (n_queries, 2), return s(i, j) for (i, j) in query as array.

Returns

predictions – The prediction scores.

Return type

int, float or array

class sknetwork.linkpred.AdamicAdar

Link prediction by Adamic-Adar index:

\(s(i, j) = \underset{z \in \Gamma_i \cap \Gamma_j}{\sum} \dfrac{1}{\log |\Gamma_z|}\).

Variables

• indptr_ (np.ndarray) – Pointer index for neighbors.

• indices_ (np.ndarray) – Concatenation of neighbors.

Examples

>>> from sknetwork.data import house
>>> adjacency = house()
>>> aa = AdamicAdar()
>>> similarities = aa.fit_predict(adjacency, 0)
>>> similarities.round(2)
array([1.82, 0.91, 0.91, 0.91, 0.91])
>>> similarities = aa.predict([0, 1])
>>> similarities.round(2)
array([[1.82, 0.91, 0.91, 0.91, 0.91],
       [0.91, 3.8 , 0.  , 2.35, 1.44]])
>>> similarities = aa.predict((0, 1))
>>> similarities.round(2)
0.91
>>> similarities = aa.predict([(0, 1), (1, 2)])
>>> similarities.round(2)
array([0.91, 0.  ])

References

Adamic, L. A., & Adar, E. (2003). Friends and neighbors on the web. Social networks, 25(3), 211-230.

fit(adjacency: Union[scipy.sparse.csr.csr_matrix, numpy.ndarray])

Fit algorithm to the data.

Parameters

adjacency – Adjacency matrix of the graph

Returns

self

Return type

FirstOrder

fit_predict(adjacency, query)

Fit algorithm to data and compute scores for requested edges.

predict(query: Union[int, Iterable, Tuple])

Compute similarity scores.

Parameters

query (int, list, array or Tuple) –

• If int i, return the similarities s(i, j) for all j.

• If list or array integers, return s(i, j) for i in query, for all j as array.

• If tuple (i, j), return the similarity s(i, j).

• If list of tuples or array of shape (n_queries, 2), return s(i, j) for (i, j) in query as array.

Returns

predictions – The prediction scores.

Return type

int, float or array

class sknetwork.linkpred.ResourceAllocation

Link prediction by Resource Allocation index:

\(s(i, j) = \underset{z \in \Gamma_i \cap \Gamma_j}{\sum} \dfrac{1}{|\Gamma_z|}\).

Variables

• indptr_ (np.ndarray) – Pointer index for neighbors.

• indices_ (np.ndarray) – Concatenation of neighbors.

Examples

>>> from sknetwork.data import house
>>> adjacency = house()
>>> ra = ResourceAllocation()
>>> similarities = ra.fit_predict(adjacency, 0)
>>> similarities.round(2)
array([0.67, 0.33, 0.33, 0.33, 0.33])
>>> similarities = ra.predict([0, 1])
>>> similarities.round(2)
array([[0.67, 0.33, 0.33, 0.33, 0.33],
       [0.33, 1.33, 0.  , 0.83, 0.5 ]])
>>> similarities = ra.predict((0, 1))
>>> similarities.round(2)
0.33
>>> similarities = ra.predict([(0, 1), (1, 2)])
>>> similarities.round(2)
array([0.33, 0.  ])

References

Zhou, T., Lü, L., & Zhang, Y. C. (2009). Predicting missing links via local information. The European Physical Journal B, 71(4), 623-630.

fit(adjacency: Union[scipy.sparse.csr.csr_matrix, numpy.ndarray])

Fit algorithm to the data.

Parameters

adjacency – Adjacency matrix of the graph

Returns

self

Return type

FirstOrder

fit_predict(adjacency, query)

Fit algorithm to data and compute scores for requested edges.

predict(query: Union[int, Iterable, Tuple])

Compute similarity scores.

Parameters

query (int, list, array or Tuple) –

• If int i, return the similarities s(i, j) for all j.

• If list or array integers, return s(i, j) for i in query, for all j as array.

• If tuple (i, j), return the similarity s(i, j).

• If list of tuples or array of shape (n_queries, 2), return s(i, j) for (i, j) in query as array.

Returns

predictions – The prediction scores.

Return type

int, float or array

class sknetwork.linkpred.PreferentialAttachment

Link prediction by Preferential Attachment index:

\(s(i, j) = |\Gamma_i||\Gamma_j|\).

Variables

• indptr_ (np.ndarray) – Pointer index for neighbors.

• indices_ (np.ndarray) – Concatenation of neighbors.

Examples

>>> from sknetwork.data import house
>>> adjacency = house()
>>> pa = PreferentialAttachment()
>>> similarities = pa.fit_predict(adjacency, 0)
>>> similarities
array([4, 6, 4, 4, 6], dtype=int32)
>>> similarities = pa.predict([0, 1])
>>> similarities
array([[4, 6, 4, 4, 6],
       [6, 9, 6, 6, 9]], dtype=int32)
>>> similarities = pa.predict((0, 1))
>>> similarities
6
>>> similarities = pa.predict([(0, 1), (1, 2)])
>>> similarities
array([6, 6], dtype=int32)

References

Albert, R., Barabási, L. (2002). Statistical mechanics of complex networks Reviews of Modern Physics.

fit(adjacency: Union[scipy.sparse.csr.csr_matrix, numpy.ndarray])

Fit algorithm to the data.

Parameters

adjacency – Adjacency matrix of the graph

Returns

self

Return type

FirstOrder

fit_predict(adjacency, query)

Fit algorithm to data and compute scores for requested edges.

predict(query: Union[int, Iterable, Tuple])

Compute similarity scores.

Parameters

query (int, list, array or Tuple) –

• If int i, return the similarities s(i, j) for all j.

• If list or array integers, return s(i, j) for i in query, for all j as array.

• If tuple (i, j), return the similarity s(i, j).

• If list of tuples or array of shape (n_queries, 2), return s(i, j) for (i, j) in query as array.

Returns

predictions – The prediction scores.

Return type

int, float or array

Post-processing

sknetwork.linkpred.is_edge(adjacency: scipy.sparse.csr.csr_matrix, query: Union[int, Iterable, Tuple]) → Union[bool, numpy.ndarray]

Given a query, return whether each edge is actually in the adjacency.

Parameters

• adjacency – Adjacency matrix of the graph.

• query (int, Iterable or Tuple) –

  • If int i, queries (i, j) for all j.

  • If Iterable of integers, return queries (i, j) for i in query, for all j.

  • If tuple (i, j), queries (i, j).

  • If list of tuples or array of shape (n_queries, 2), queries (i, j) in for each line in query.

Returns

y_true – For each element in the query, returns True if the edge exists in the adjacency and False otherwise.

Return type

Union[bool, np.ndarray]

Examples

>>> from sknetwork.data import house
>>> adjacency = house()
>>> is_edge(adjacency, 0)
array([False,  True, False, False,  True])
>>> is_edge(adjacency, [0, 1])
array([[False,  True, False, False,  True],
       [ True, False,  True, False,  True]])
>>> is_edge(adjacency, (0, 1))
True
>>> is_edge(adjacency, [(0, 1), (0, 2)])
array([ True, False])

sknetwork.linkpred.whitened_sigmoid(scores: numpy.ndarray)

Map the entries of a score array to probabilities through

\(\dfrac{1}{1 + \exp(-(x - \mu)/\sigma)}\),

where \(\mu\) and \(\sigma\) are respectively the mean and standard deviation of x.

Parameters

scores (np.ndarray) – The input array

Returns

probas – Array with entries between 0 and 1.

Return type

np.ndarray

Examples

>>> probas = whitened_sigmoid(np.array([1, 5, 0.25]))
>>> probas.round(2)
array([0.37, 0.8 , 0.29])
>>> probas = whitened_sigmoid(np.array([2, 2, 2]))
>>> probas
array([1, 1, 1])