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similarities.pyx
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similarities.pyx
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"""
The :mod:`similarities <surprise.similarities>` module includes tools to
compute similarity metrics between users or items. You may need to refer to the
:ref:`notation_standards` page. See also the
:ref:`similarity_measures_configuration` section of the User Guide.
Available similarity measures:
.. autosummary::
:nosignatures:
cosine
msd
pearson
pearson_baseline
"""
from __future__ import (absolute_import, division, print_function,
unicode_literals)
cimport numpy as np # noqa
import numpy as np
from six.moves import range
from six import iteritems
def cosine(n_x, yr, min_support):
"""Compute the cosine similarity between all pairs of users (or items).
Only **common** users (or items) are taken into account. The cosine
similarity is defined as:
.. math::
\\text{cosine_sim}(u, v) = \\frac{
\\sum\\limits_{i \in I_{uv}} r_{ui} \cdot r_{vi}}
{\\sqrt{\\sum\\limits_{i \in I_{uv}} r_{ui}^2} \cdot
\\sqrt{\\sum\\limits_{i \in I_{uv}} r_{vi}^2}
}
or
.. math::
\\text{cosine_sim}(i, j) = \\frac{
\\sum\\limits_{u \in U_{ij}} r_{ui} \cdot r_{uj}}
{\\sqrt{\\sum\\limits_{u \in U_{ij}} r_{ui}^2} \cdot
\\sqrt{\\sum\\limits_{u \in U_{ij}} r_{uj}^2}
}
depending on the ``user_based`` field of ``sim_options`` (see
:ref:`similarity_measures_configuration`).
For details on cosine similarity, see on `Wikipedia
<https://en.wikipedia.org/wiki/Cosine_similarity#Definition>`__.
"""
# sum (r_xy * r_x'y) for common ys
cdef np.ndarray[np.int_t, ndim=2] prods
# number of common ys
cdef np.ndarray[np.int_t, ndim=2] freq
# sum (r_xy ^ 2) for common ys
cdef np.ndarray[np.int_t, ndim=2] sqi
# sum (r_x'y ^ 2) for common ys
cdef np.ndarray[np.int_t, ndim=2] sqj
# the similarity matrix
cdef np.ndarray[np.double_t, ndim=2] sim
cdef int xi, xj, ri, rj
cdef int min_sprt = min_support
prods = np.zeros((n_x, n_x), np.int)
freq = np.zeros((n_x, n_x), np.int)
sqi = np.zeros((n_x, n_x), np.int)
sqj = np.zeros((n_x, n_x), np.int)
sim = np.zeros((n_x, n_x), np.double)
for y, y_ratings in iteritems(yr):
for xi, ri in y_ratings:
for xj, rj in y_ratings:
freq[xi, xj] += 1
prods[xi, xj] += ri * rj
sqi[xi, xj] += ri**2
sqj[xi, xj] += rj**2
for xi in range(n_x):
sim[xi, xi] = 1
for xj in range(xi + 1, n_x):
if freq[xi, xj] < min_sprt:
sim[xi, xj] = 0
else:
denum = np.sqrt(sqi[xi, xj] * sqj[xi, xj])
sim[xi, xj] = prods[xi, xj] / denum
sim[xj, xi] = sim[xi, xj]
return sim
def msd(n_x, yr, min_support):
"""Compute the Mean Squared Difference similarity between all pairs of
users (or items).
Only **common** users (or items) are taken into account. The Mean Squared
Difference is defined as:
.. math ::
\\text{msd}(u, v) = \\frac{1}{|I_{uv}|} \cdot
\\sum\\limits_{i \in I_{uv}} (r_{ui} - r_{vi})^2
or
.. math ::
\\text{msd}(i, j) = \\frac{1}{|U_{ij}|} \cdot
\\sum\\limits_{u \in U_{ij}} (r_{ui} - r_{uj})^2
depending on the ``user_based`` field of ``sim_options`` (see
:ref:`similarity_measures_configuration`).
The MSD-similarity is then defined as:
.. math ::
\\text{msd_sim}(u, v) &= \\frac{1}{\\text{msd}(u, v) + 1}\\\\
\\text{msd_sim}(i, j) &= \\frac{1}{\\text{msd}(i, j) + 1}
The :math:`+ 1` term is just here to avoid dividing by zero.
For details on MSD, see third definition on `Wikipedia
<https://en.wikipedia.org/wiki/Root-mean-square_deviation#Formula>`__.
"""
# sum (r_xy - r_x'y)**2 for common ys
cdef np.ndarray[np.double_t, ndim=2] sq_diff
# number of common ys
cdef np.ndarray[np.int_t, ndim=2] freq
# the similarity matrix
cdef np.ndarray[np.double_t, ndim=2] sim
cdef int xi, xj, ri, rj
cdef int min_sprt = min_support
sq_diff = np.zeros((n_x, n_x), np.double)
freq = np.zeros((n_x, n_x), np.int)
sim = np.zeros((n_x, n_x), np.double)
for y, y_ratings in iteritems(yr):
for xi, ri in y_ratings:
for xj, rj in y_ratings:
sq_diff[xi, xj] += (ri - rj)**2
freq[xi, xj] += 1
for xi in range(n_x):
sim[xi, xi] = 1 # completely arbitrary and useless anyway
for xj in range(xi + 1, n_x):
if freq[xi, xj] < min_sprt:
sim[xi, xj] == 0
else:
# return inverse of (msd + 1) (+ 1 to avoid dividing by zero)
sim[xi, xj] = 1 / (sq_diff[xi, xj] / freq[xi, xj] + 1)
sim[xj, xi] = sim[xi, xj]
return sim
def pearson(n_x, yr, min_support):
"""Compute the Pearson correlation coefficient between all pairs of users
(or items).
Only **common** users (or items) are taken into account. The Pearson
correlation coefficient can be seen as a mean-centered cosine similarity,
and is defined as:
.. math ::
\\text{pearson_sim}(u, v) = \\frac{ \\sum\\limits_{i \in I_{uv}}
(r_{ui} - \mu_u) \cdot (r_{vi} - \mu_{v})} {\\sqrt{\\sum\\limits_{i
\in I_{uv}} (r_{ui} - \mu_u)^2} \cdot \\sqrt{\\sum\\limits_{i \in
I_{uv}} (r_{vi} - \mu_{v})^2} }
or
.. math ::
\\text{pearson_sim}(i, j) = \\frac{ \\sum\\limits_{u \in U_{ij}}
(r_{ui} - \mu_i) \cdot (r_{uj} - \mu_{j})} {\\sqrt{\\sum\\limits_{u
\in U_{ij}} (r_{ui} - \mu_i)^2} \cdot \\sqrt{\\sum\\limits_{u \in
U_{ij}} (r_{uj} - \mu_{j})^2} }
depending on the ``user_based`` field of ``sim_options`` (see
:ref:`similarity_measures_configuration`).
Note: if there are no common users or items, similarity will be 0 (and not
-1).
For details on Pearson coefficient, see `Wikipedia
<https://en.wikipedia.org/wiki/Pearson_product-moment_correlation_coefficient#For_a_sample>`__.
"""
# number of common ys
cdef np.ndarray[np.int_t, ndim=2] freq
# sum (r_xy * r_x'y) for common ys
cdef np.ndarray[np.int_t, ndim=2] prods
# sum (rxy ^ 2) for common ys
cdef np.ndarray[np.int_t, ndim=2] sqi
# sum (rx'y ^ 2) for common ys
cdef np.ndarray[np.int_t, ndim=2] sqj
# sum (rxy) for common ys
cdef np.ndarray[np.int_t, ndim=2] si
# sum (rx'y) for common ys
cdef np.ndarray[np.int_t, ndim=2] sj
# the similarity matrix
cdef np.ndarray[np.double_t, ndim=2] sim
cdef int xi, xj, ri, rj
cdef int min_sprt = min_support
freq = np.zeros((n_x, n_x), np.int)
prods = np.zeros((n_x, n_x), np.int)
sqi = np.zeros((n_x, n_x), np.int)
sqj = np.zeros((n_x, n_x), np.int)
si = np.zeros((n_x, n_x), np.int)
sj = np.zeros((n_x, n_x), np.int)
sim = np.zeros((n_x, n_x), np.double)
for y, y_ratings in iteritems(yr):
for xi, ri in y_ratings:
for xj, rj in y_ratings:
prods[xi, xj] += ri * rj
freq[xi, xj] += 1
sqi[xi, xj] += ri**2
sqj[xi, xj] += rj**2
si[xi, xj] += ri
sj[xi, xj] += rj
for xi in range(n_x):
sim[xi, xi] = 1
for xj in range(xi + 1, n_x):
if freq[xi, xj] < min_sprt:
sim[xi, xj] == 0
else:
n = freq[xi, xj]
num = n * prods[xi, xj] - si[xi, xj] * sj[xi, xj]
denum = np.sqrt((n * sqi[xi, xj] - si[xi, xj]**2) *
(n * sqj[xi, xj] - sj[xi, xj]**2))
if denum == 0:
sim[xi, xj] = 0
else:
sim[xi, xj] = num / denum
sim[xj, xi] = sim[xi, xj]
return sim
def pearson_baseline(n_x, yr, min_support, global_mean, x_biases, y_biases,
shrinkage=100):
"""Compute the (shrunk) Pearson correlation coefficient between all pairs
of users (or items) using baselines for centering instead of means.
The shrinkage parameter helps to avoid overfitting when only few ratings
are available (see :ref:`similarity_measures_configuration`).
The Pearson-baseline correlation coefficient is defined as:
.. math::
\\text{pearson_baseline_sim}(u, v) = \hat{\\rho}_{uv} = \\frac{
\\sum\\limits_{i \in I_{uv}} (r_{ui} - b_{ui}) \cdot (r_{vi} -
b_{vi})} {\\sqrt{\\sum\\limits_{i \in I_{uv}} (r_{ui} - b_{ui})^2}
\cdot \\sqrt{\\sum\\limits_{i \in I_{uv}} (r_{vi} - b_{vi})^2}}
or
.. math::
\\text{pearson_baseline_sim}(i, j) = \hat{\\rho}_{ij} = \\frac{
\\sum\\limits_{u \in U_{ij}} (r_{ui} - b_{ui}) \cdot (r_{uj} -
b_{uj})} {\\sqrt{\\sum\\limits_{u \in U_{ij}} (r_{ui} - b_{ui})^2}
\cdot \\sqrt{\\sum\\limits_{u \in U_{ij}} (r_{uj} - b_{uj})^2}}
The shrunk Pearson-baseline correlation coefficient is then defined as:
.. math::
\\text{pearson_baseline_shrunk_sim}(u, v) &= \\frac{|I_{uv}| - 1}
{|I_{uv}| - 1 + \\text{shrinkage}} \\cdot \hat{\\rho}_{uv}
\\text{pearson_baseline_shrunk_sim}(i, j) &= \\frac{|U_{ij}| - 1}
{|U_{ij}| - 1 + \\text{shrinkage}} \\cdot \hat{\\rho}_{ij}
Obviously, a shrinkage parameter of 0 amounts to no shrinkage at all.
Note: here again, if there are no common users/items, similarity will be 0
(and not -1).
Motivations for such a similarity measure can be found on the *Recommender
System Handbook*, section 5.4.1.
"""
# number of common ys
cdef np.ndarray[np.int_t, ndim=2] freq
# sum (r_xy - b_xy) * (r_x'y - b_x'y) for common ys
cdef np.ndarray[np.double_t, ndim=2] prods
# sum (r_xy - b_xy)**2 for common ys
cdef np.ndarray[np.double_t, ndim=2] sq_diff_i
# sum (r_x'y - b_x'y)**2 for common ys
cdef np.ndarray[np.double_t, ndim=2] sq_diff_j
# the similarity matrix
cdef np.ndarray[np.double_t, ndim=2] sim
cdef np.ndarray[np.double_t, ndim=1] x_biases_
cdef np.ndarray[np.double_t, ndim=1] y_biases_
cdef int xi, xj
cdef double ri, rj, diff_i, diff_j, partial_bias
cdef int min_sprt = min_support
cdef double global_mean_ = global_mean
freq = np.zeros((n_x, n_x), np.int)
prods = np.zeros((n_x, n_x), np.double)
sq_diff_i = np.zeros((n_x, n_x), np.double)
sq_diff_j = np.zeros((n_x, n_x), np.double)
sim = np.zeros((n_x, n_x), np.double)
x_biases_ = x_biases
y_biases_ = y_biases
# Need this because of shrinkage. When pearson coeff is zero when support
# is 1, so that's OK.
min_sprt = max(2, min_sprt)
for y, y_ratings in iteritems(yr):
partial_bias = global_mean_ + y_biases_[y]
for xi, ri in y_ratings:
for xj, rj in y_ratings:
freq[xi, xj] += 1
diff_i = (ri - (partial_bias + x_biases_[xi]))
diff_j = (rj - (partial_bias + x_biases_[xj]))
prods[xi, xj] += diff_i * diff_j
sq_diff_i[xi, xj] += diff_i**2
sq_diff_j[xi, xj] += diff_j**2
for xi in range(n_x):
sim[xi, xi] = 1
for xj in range(xi + 1, n_x):
if freq[xi, xj] < min_sprt:
sim[xi, xj] = 0
else:
sim[xi, xj] = prods[xi, xj] / (np.sqrt(sq_diff_i[xi, xj] *
sq_diff_j[xi, xj]))
# the shrinkage part
sim[xi, xj] *= (freq[xi, xj] - 1) / (freq[xi, xj] - 1 +
shrinkage)
sim[xj, xi] = sim[xi, xj]
return sim