import numpy as np
from .strategy import Strategy
from sklearn.cluster import KMeans
[docs]class KMeansSampling(Strategy):
"""
Implementation of KMeans Sampling Strategy.
This class extends :class:`active_learning_strategies.strategy.Strategy`
to include entropy sampling technique to select data points for active learning.
In KMeans Sampling selection strategy, the last layer embeddings are calculated for all the unlabeled data points.
Then the KMeans clustering algorithm is run over these embeddings with the number of clusters equal to the budget.
Then the distance is calculated for all the points from their respective centers.
From each cluster, the point closest to the center is selected to be labeled for the next iteration.
Since the number of centers are equal to the budget, selecting one point from each cluster satisfies the total number of data points to be selected in one iteration.
Let :math:`d_i` represent distance of a point from the center of a cluster and D represent the set of distances for all the points that belong to a particular cluster, then Mathematically,
.. math::
\\min{(D)}
where :math:`D=[d_1,d_2...d_n]` where n is the number of points in a given cluster
Parameters
----------
X: numpy array
Present training/labeled data
y: numpy array
Labels of present training data
unlabeled_x: numpy array
Data without labels
net: class
Pytorch Model class
handler: class
Data Handler, which can load data even without labels.
nclasses: int
Number of unique target variables
args: dict
Specify optional parameters
batch_size
Batch size to be used inside strategy class (int, optional)
"""
def __init__(self, X, Y, unlabeled_x, net, handler, nclasses, args={}):
"""
Constructor method
"""
super(KMeansSampling, self).__init__(X, Y, unlabeled_x, net, handler, nclasses, args={})
[docs] def select(self, budget):
"""
Select next set of points
Parameters
----------
budget: int
Nuber of indexes to be returned for next set
Returns
----------
q_idxs: list
List of selected data point indexes with respect to unlabeled_x
"""
embedding = self.get_embedding(self.unlabeled_x)
embedding = embedding.numpy()
cluster_learner = KMeans(n_clusters=budget)
cluster_learner.fit(embedding)
cluster_idxs = cluster_learner.predict(embedding)
centers = cluster_learner.cluster_centers_[cluster_idxs]
dis = (embedding - centers)**2
dis = dis.sum(axis=1)
q_idxs = np.array([np.arange(embedding.shape[0])[cluster_idxs==i][dis[cluster_idxs==i].argmin()] for i in range(budget)])
return q_idxs