# Source code for metric_learn.scml

"""
Sparse Compositional Metric Learning (SCML)
"""

from __future__ import print_function, absolute_import, division
import numpy as np
from .base_metric import _TripletsClassifierMixin, MahalanobisMixin
from ._util import components_from_metric
from sklearn.base import TransformerMixin
from .constraints import Constraints
from sklearn.preprocessing import normalize
from sklearn.neighbors import NearestNeighbors
from sklearn.cluster import KMeans
from sklearn.discriminant_analysis import LinearDiscriminantAnalysis
from sklearn.utils import check_array, check_random_state
import warnings

class _BaseSCML(MahalanobisMixin):

_tuple_size = 3   # constraints are triplets
_authorized_basis = ['triplet_diffs']

def __init__(self, beta=1e-5, basis='triplet_diffs', n_basis=None,
gamma=5e-3, max_iter=10000, output_iter=500, batch_size=10,
verbose=False, preprocessor=None, random_state=None):
self.beta = beta
self.basis = basis
self.n_basis = n_basis
self.gamma = gamma
self.max_iter = max_iter
self.output_iter = output_iter
self.batch_size = batch_size
self.verbose = verbose
self.preprocessor = preprocessor
self.random_state = random_state
super(_BaseSCML, self).__init__(preprocessor)

def _fit(self, triplets, basis=None, n_basis=None):
"""
Optimization procedure to find a sparse vector of weights to
construct the metric from the basis set. This is based on the
dual averaging method.
"""

if not isinstance(self.max_iter, int):
raise ValueError("max_iter should be an integer, instead it is of type"
" %s" % type(self.max_iter))
if not isinstance(self.output_iter, int):
raise ValueError("output_iter should be an integer, instead it is of "
"type %s" % type(self.output_iter))
if not isinstance(self.batch_size, int):
raise ValueError("batch_size should be an integer, instead it is of type"
" %s" % type(self.batch_size))

if(self.output_iter > self.max_iter):
raise ValueError("The value of output_iter must be equal or smaller than"
" max_iter.")

# Currently prepare_inputs makes triplets contain points and not indices
triplets = self._prepare_inputs(triplets, type_of_inputs='tuples')

# TODO:
# This algorithm is built to work with indices, but in order to be
# compliant with the current handling of inputs it is converted
# back to indices by the following function. This should be improved
# in the future.
triplets, X = self._to_index_points(triplets)

if basis is None:
basis, n_basis = self._initialize_basis(triplets, X)

dist_diff = self._compute_dist_diff(triplets, X, basis)

n_triplets = triplets.shape

# weight vector
w = np.zeros((1, n_basis))
# avarage obj gradient wrt weights

# l2 norm in time of all obj gradients wrt weights
# slack for not dividing by zero
delta = 0.001

best_obj = np.inf

rng = check_random_state(self.random_state)
rand_int = rng.randint(low=0, high=n_triplets,
size=(self.max_iter, self.batch_size))
for iter in range(self.max_iter):

idx = rand_int[iter]

slack_val = 1 + np.matmul(dist_diff[idx, :], w.T)
slack_mask = np.squeeze(slack_val > 0, axis=1)

axis=0, keepdims=True)/self.batch_size

# proximal operator with negative trimming equivalent
w = scale_f * np.minimum(avg_grad_w + self.beta, 0)

if (iter + 1) % self.output_iter == 0:
# regularization part of obj function
obj1 = np.sum(w)*self.beta

# Every triplet distance difference in the space given by L
# plus a slack of one
slack_val = 1 + np.matmul(dist_diff, w.T)
# Mask of places with positive slack

# loss function of learning task part of obj function

obj = obj1 + obj2
if self.verbose:
print("[%s] iter %d\t obj %.6f\t num_imp %d" %
(self.__class__.__name__, (iter+1), obj, count))

# update the best
if obj < best_obj:
best_obj = obj
best_w = w

if self.verbose:
print("max iteration reached.")

# return L matrix yielded from best weights
self.n_iter_ = iter
self.components_ = self._components_from_basis_weights(basis, best_w)

return self

def _compute_dist_diff(self, triplets, X, basis):
"""
Helper function to compute the distance difference of every triplet in the
space yielded by the basis set.
"""
# Transformation of data by the basis set
XB = np.matmul(X, basis.T)

n_triplets = triplets.shape
# get all positive and negative pairs with lowest index first
# np.array (2*n_triplets,2)
triplets_pairs_sorted = np.sort(np.vstack((triplets[:, [0, 1]],
triplets[:, [0, 2]])),
kind='stable')
# calculate all unique pairs and their indices
uniqPairs, indices = np.unique(triplets_pairs_sorted, return_inverse=True,
axis=0)
# calculate L2 distance acording to bases only for unique pairs
dist = np.square(XB[uniqPairs[:, 0], :] - XB[uniqPairs[:, 1], :])

# return the diference of distances between all positive and negative
# pairs
return dist[indices[:n_triplets]] - dist[indices[n_triplets:]]

def _components_from_basis_weights(self, basis, w):
"""
Get components matrix (L) from computed mahalanobis matrix.
"""

# get rid of inactive bases
# TODO: Maybe have a tolerance over zero?
active_idx, = w > 0
w = w[..., active_idx]
basis = basis[active_idx, :]

n_basis, n_features = basis.shape

if n_basis < n_features:  # if metric is low-rank
warnings.warn("The number of bases with nonzero weight is less than the "
"number of features of the input, in consequence the "
"learned transformation reduces the dimension to %d."
% n_basis)
return np.sqrt(w.T)*basis  # equivalent to np.diag(np.sqrt(w)).dot(basis)

else:   # if metric is full rank
return components_from_metric(np.matmul(basis.T, w.T*basis))

def _to_index_points(self, triplets):
shape = triplets.shape
X, triplets = np.unique(np.vstack(triplets), return_inverse=True, axis=0)
triplets = triplets.reshape(shape[:2])
return triplets, X

def _initialize_basis(self, triplets, X):
""" Checks if the basis array is well constructed or constructs it based
on one of the available options.
"""
n_features = X.shape

if isinstance(self.basis, np.ndarray):
# TODO: should copy?
basis = check_array(self.basis, copy=True)
if basis.shape != n_features:
raise ValueError('The dimensionality ({}) of the provided bases must'
' match the dimensionality of the data '
'({}).'.format(basis.shape, n_features))
elif self.basis not in self._authorized_basis:
raise ValueError(
"basis must be one of the options '{}' "
"or an array of shape (n_basis, n_features)."
.format("', '".join(self._authorized_basis)))
if self.basis == 'triplet_diffs':
basis, n_basis = self._generate_bases_dist_diff(triplets, X)

return basis, n_basis

def _generate_bases_dist_diff(self, triplets, X):
""" Constructs the basis set from the differences of positive and negative
pairs from the triplets constraints.

The basis set is constructed iteratively by taking n_features triplets,
then adding and substracting respectively all the outerproducts of the
positive and negative pairs, and finally selecting the eigenvectors
of this matrix with positive eigenvalue. This is done until n_basis are
selected.
"""
n_features = X.shape
n_triplets = triplets.shape

if self.n_basis is None:
# TODO: Get a good default n_basis directive
n_basis = n_features*80
warnings.warn('As no value for n_basis was selected, the number of '
'basis will be set to n_basis= %d' % n_basis)
elif isinstance(self.n_basis, int):
n_basis = self.n_basis
else:
raise ValueError("n_basis should be an integer, instead it is of type %s"
% type(self.n_basis))

basis = np.zeros((n_basis, n_features))

# get all positive and negative pairs with lowest index first
# np.array (2*n_triplets,2)
triplets_pairs_sorted = np.sort(np.vstack((triplets[:, [0, 1]],
triplets[:, [0, 2]])),
kind='stable')
# calculate all unique pairs and their indices
uniqPairs, indices = np.unique(triplets_pairs_sorted, return_inverse=True,
axis=0)
# calculate differences only for unique pairs
diff = X[uniqPairs[:, 0], :] - X[uniqPairs[:, 1], :]

diff_pos = diff[indices[:n_triplets], :]
diff_neg = diff[indices[n_triplets:], :]

rng = check_random_state(self.random_state)

start = 0
finish = 0

while(finish != n_basis):

# Select triplets to yield diff

select_triplet = rng.choice(n_triplets, size=n_features, replace=False)

# select n_features positive differences
d_pos = diff_pos[select_triplet, :]

# select n_features negative differences
d_neg = diff_neg[select_triplet, :]

# Yield matrix
diff_sum = d_pos.T.dot(d_pos) - d_neg.T.dot(d_neg)

# Calculate eigenvalue and eigenvectors
w, v = np.linalg.eigh(diff_sum.T.dot(diff_sum))

# Add eigenvectors with positive eigenvalue to basis set
start = finish

try:
except ValueError:
# if finish is greater than n_basis
break

# TODO: maybe add a warning in case there are no added bases, this could
# be caused by a bad triplet set. This would cause an infinite loop

return basis, n_basis

[docs]class SCML(_BaseSCML, _TripletsClassifierMixin):
"""Sparse Compositional Metric Learning (SCML)

SCML learns an squared Mahalanobis distance from triplet constraints by
optimizing sparse positive weights assigned to a set of :math:K rank-one
PSD bases. This can be formulated as an optimization problem with only
:math:K parameters, that can be solved with an efficient stochastic
composite scheme.

Read more in the :ref:User Guide <scml>.

.. warning::
SCML is still a bit experimental, don't hesitate to report if
something fails/doesn't work as expected.

Parameters
----------
beta: float (default=1e-5)
L1 regularization parameter.

basis : string or array-like, optional (default='triplet_diffs')
Set of bases to construct the metric. Possible options are
'triplet_diffs', and an array-like of shape (n_basis, n_features).

'triplet_diffs'
The basis set is constructed from the differences between points of
n_basis positive or negative pairs taken from the triplets
constrains.

array-like
A matrix of shape (n_basis, n_features), that will be used as
the basis set for the metric construction.

n_basis : int, optional
Number of basis to be yielded. In case it is not set it will be set based
on basis. If no value is selected a default will be computed based on
the input.

gamma: float (default = 5e-3)
Learning rate for the optimization algorithm.

max_iter : int (default = 100000)
Number of iterations for the algorithm.

output_iter : int (default = 5000)
Number of iterations to check current weights performance and output this
information in case verbose is True.

verbose : bool, optional
If True, prints information while learning.

preprocessor : array-like, shape=(n_samples, n_features) or callable
The preprocessor to call to get triplets from indices. If array-like,
triplets will be formed like this: X[indices].

random_state : int or numpy.RandomState or None, optional (default=None)
A pseudo random number generator object or a seed for it if int.

Attributes
----------
components_ : numpy.ndarray, shape=(n_features, n_features)
The linear transformation L deduced from the learned Mahalanobis
metric (See function _components_from_basis_weights.)

Examples
--------
>>> from metric_learn import SCML
>>> triplets = [[[1.2, 7.5], [1.3, 1.5], [6.2, 9.7]],
>>>             [[1.3, 4.5], [3.2, 4.6], [5.4, 5.4]],
>>>             [[3.2, 7.5], [3.3, 1.5], [8.2, 9.7]],
>>>             [[3.3, 4.5], [5.2, 4.6], [7.4, 5.4]]]
>>> scml = SCML()
>>> scml.fit(triplets)

References
----------
..  Y. Shi, A. Bellet and F. Sha. Sparse Compositional Metric Learning.
<http://researchers.lille.inria.fr/abellet/papers/aaai14.pdf>_. \
(AAAI), 2014.

..  Adapted from original \
Matlab implementation.<https://github.com/bellet/SCML>_.

--------
metric_learn.SCML_Supervised : The supervised version of the algorithm.

:ref:supervised_version : The section of the project documentation
that describes the supervised version of weakly supervised estimators.
"""

[docs]  def fit(self, triplets):
"""Learn the SCML model.

Parameters
----------
triplets : array-like, shape=(n_constraints, 3, n_features) or \
(n_constraints, 3)
3D array-like of triplets of points or 2D array of triplets of
indicators. Triplets are assumed to be ordered such that:
d(triplets[i, 0],triplets[i, 1]) < d(triplets[i, 0], triplets[i, 2]).

Returns
-------
self : object
Returns the instance.
"""

return self._fit(triplets)

[docs]class SCML_Supervised(_BaseSCML, TransformerMixin):
"""Supervised version of Sparse Compositional Metric Learning (SCML)

SCML_Supervised creates triplets by taking k_genuine neighbours
of the same class and k_impostor neighbours from different classes for each
point and then runs the SCML algorithm on these triplets.

Read more in the :ref:User Guide <scml>.

.. warning::
SCML is still a bit experimental, don't hesitate to report if
something fails/doesn't work as expected.

Parameters
----------
beta: float (default=1e-5)
L1 regularization parameter.

basis : string or an array-like, optional (default='lda')
Set of bases to construct the metric. Possible options are
'lda', and an array-like of shape (n_basis, n_features).

'lda'
The n_basis basis set is constructed from the LDA of significant
local regions in the feature space via clustering, for each region
center k-nearest neighbors are used to obtain the LDA scalings,
which correspond to the locally discriminative basis.

array-like
A matrix of shape (n_basis, n_features), that will be used as
the basis set for the metric construction.

n_basis : int, optional
Number of basis to be yielded. In case it is not set it will be set based
on basis. If no value is selected a default will be computed based on
the input.

gamma: float (default = 5e-3)
Learning rate for the optimization algorithm.

max_iter : int (default = 100000)
Number of iterations for the algorithm.

output_iter : int (default = 5000)
Number of iterations to check current weights performance and output this
information in case verbose is True.

verbose : bool, optional
If True, prints information while learning.

preprocessor : array-like, shape=(n_samples, n_features) or callable
The preprocessor to call to get triplets from indices. If array-like,
triplets will be formed like this: X[indices].

random_state : int or numpy.RandomState or None, optional (default=None)
A pseudo random number generator object or a seed for it if int.

Attributes
----------
components_ : numpy.ndarray, shape=(n_features, n_features)
The linear transformation L deduced from the learned Mahalanobis
metric (See function _components_from_basis_weights.)

Examples
--------
>>> from metric_learn import SCML
>>> triplets = np.array([[[1.2, 3.2], [2.3, 5.5], [2.1, 0.6]],
>>>                      [[4.5, 2.3], [2.1, 2.3], [7.3, 3.4]]])
>>> scml = SCML(random_state=42)
>>> scml.fit(triplets)
SCML(beta=1e-5, B=None, max_iter=100000, verbose=False,
preprocessor=None, random_state=None)

References
----------
..  Y. Shi, A. Bellet and F. Sha. Sparse Compositional Metric Learning.
<http://researchers.lille.inria.fr/abellet/papers/aaai14.pdf>_. \
(AAAI), 2014.

..  Adapted from original \
Matlab implementation.<https://github.com/bellet/SCML>_.

--------
metric_learn.SCML : The weakly supervised version of this
algorithm.
"""
# Add supervised authorized basis construction options
_authorized_basis = _BaseSCML._authorized_basis + ['lda']

[docs]  def __init__(self, k_genuine=3, k_impostor=10, beta=1e-5, basis='lda',
n_basis=None, gamma=5e-3, max_iter=10000, output_iter=500,
batch_size=10, verbose=False, preprocessor=None,
random_state=None):
self.k_genuine = k_genuine
self.k_impostor = k_impostor
_BaseSCML.__init__(self, beta=beta, basis=basis, n_basis=n_basis,
max_iter=max_iter, output_iter=output_iter,
batch_size=batch_size, verbose=verbose,
preprocessor=preprocessor, random_state=random_state)

[docs]  def fit(self, X, y):
"""Create constraints from labels and learn the SCML model.

Parameters
----------
X : (n x d) matrix
Input data, where each row corresponds to a single instance.

y : (n) array-like
Data labels.

Returns
-------
self : object
Returns the instance.
"""
X, y = self._prepare_inputs(X, y, ensure_min_samples=2)

basis, n_basis = self._initialize_basis_supervised(X, y)

if not isinstance(self.k_genuine, int):
raise ValueError("k_genuine should be an integer, instead it is of type"
" %s" % type(self.k_genuine))
if not isinstance(self.k_impostor, int):
raise ValueError("k_impostor should be an integer, instead it is of "
"type %s" % type(self.k_impostor))

constraints = Constraints(y)
triplets = constraints.generate_knntriplets(X, self.k_genuine,
self.k_impostor)

triplets = X[triplets]

return self._fit(triplets, basis, n_basis)

def _initialize_basis_supervised(self, X, y):
""" Constructs the basis set following one of the supervised options in
case one is selected.
"""

if self.basis == 'lda':
basis, n_basis = self._generate_bases_LDA(X, y)
else:
basis, n_basis = None, None

return basis, n_basis

def _generate_bases_LDA(self, X, y):
""" Generates bases for the 'lda' option.

The basis set is constructed using Linear Discriminant Analysis of
significant local regions in the feature space via clustering, for
each region center k-nearest neighbors are used to obtain the LDA scalings,
which correspond to the locally discriminative basis. Currently this is
done at two scales k={10,20} if n_feature < 50 or else k={20,50}.
"""

labels, class_count = np.unique(y, return_counts=True)
n_class = len(labels)

n_features = X.shape
# Number of basis yielded from each LDA
num_eig = min(n_class-1, n_features)

if self.n_basis is None:
# TODO: Get a good default n_basis directive
n_basis = min(20*n_features, X.shape*2*num_eig - 1)
warnings.warn('As no value for n_basis was selected, the number of '
'basis will be set to n_basis= %d' % n_basis)

elif isinstance(self.n_basis, int):
n_basis = self.n_basis
else:
raise ValueError("n_basis should be an integer, instead it is of type %s"
% type(self.n_basis))

# Number of clusters needed for 2 scales given the number of basis
# yielded by every LDA
n_clusters = int(np.ceil(n_basis/(2 * num_eig)))

if n_basis < n_class:
warnings.warn("The number of basis is less than the number of classes, "
"which may lead to poor discriminative performance.")
elif n_basis >= X.shape*2*num_eig:
raise ValueError("Not enough samples to generate %d LDA bases, n_basis"
"should be smaller than %d" %
(n_basis, X.shape*2*num_eig))

kmeans = KMeans(n_clusters=n_clusters, random_state=self.random_state,
algorithm='elkan').fit(X)
cX = kmeans.cluster_centers_

n_scales = 2
if n_features > 50:
scales = [20, 50]
else:
scales = [10, 20]

k_class = np.vstack((np.minimum(class_count, scales),
np.minimum(class_count, scales)))

idx_set = [np.zeros((n_clusters, sum(k_class[0, :])), dtype=np.int),
np.zeros((n_clusters, sum(k_class[1, :])), dtype=np.int)]

start_finish_indices = np.hstack((np.zeros((2, 1), np.int),
k_class)).cumsum(axis=1)

neigh = NearestNeighbors()

for c in range(n_class):
sel_c = np.where(y == labels[c])

# get k_class same class neighbors
neigh.fit(X=X[sel_c])
# Only take the neighbors once for the biggest scale
neighbors = neigh.kneighbors(X=cX, n_neighbors=k_class[-1, c],
return_distance=False)

# add index set of neighbors for every cluster center for both scales
for s, k in enumerate(k_class[:, c]):
start, finish = start_finish_indices[s, c:c+2]
idx_set[s][:, start:finish] = np.take(sel_c, neighbors[:, :k])

# Compute basis for every cluster in both scales
basis = np.zeros((n_basis, n_features))
lda = LinearDiscriminantAnalysis()
start_finish_indices = np.hstack((np.vstack((0, n_clusters * num_eig)),
np.full((2, n_clusters),
num_eig))).cumsum(axis=1)

for s in range(n_scales):
for c in range(n_clusters):
lda.fit(X[idx_set[s][c, :]], y[idx_set[s][c, :]])
start, finish = start_finish_indices[s, c:c+2]
normalized_scalings = normalize(lda.scalings_.T)
try:
basis[start: finish, :] = normalized_scalings
except ValueError:
# handle tail
basis[start:, :] = normalized_scalings[:n_basis-start]
break

return basis, n_basis