149 research outputs found
Greedy Strategy Works for k-Center Clustering with Outliers and Coreset Construction
We study the problem of k-center clustering with outliers in arbitrary metrics and Euclidean space. Though a number of methods have been developed in the past decades, it is still quite challenging to design quality guaranteed algorithm with low complexity for this problem. Our idea is inspired by the greedy method, Gonzalez\u27s algorithm, for solving the problem of ordinary k-center clustering. Based on some novel observations, we show that this greedy strategy actually can handle k-center clustering with outliers efficiently, in terms of clustering quality and time complexity. We further show that the greedy approach yields small coreset for the problem in doubling metrics, so as to reduce the time complexity significantly. Our algorithms are easy to implement in practice. We test our method on both synthetic and real datasets. The experimental results suggest that our algorithms can achieve near optimal solutions and yield lower running times comparing with existing methods
On Coresets for Fair Clustering in Metric and Euclidean Spaces and Their Applications
Fair clustering is a constrained variant of clustering where the goal is to
partition a set of colored points, such that the fraction of points of any
color in every cluster is more or less equal to the fraction of points of this
color in the dataset. This variant was recently introduced by Chierichetti et
al. [NeurIPS, 2017] in a seminal work and became widely popular in the
clustering literature. In this paper, we propose a new construction of coresets
for fair clustering based on random sampling. The new construction allows us to
obtain the first coreset for fair clustering in general metric spaces. For
Euclidean spaces, we obtain the first coreset whose size does not depend
exponentially on the dimension. Our coreset results solve open questions
proposed by Schmidt et al. [WAOA, 2019] and Huang et al. [NeurIPS, 2019]. The
new coreset construction helps to design several new approximation and
streaming algorithms. In particular, we obtain the first true
constant-approximation algorithm for metric fair clustering, whose running time
is fixed-parameter tractable (FPT). In the Euclidean case, we derive the first
-approximation algorithm for fair clustering whose time
complexity is near-linear and does not depend exponentially on the dimension of
the space. Besides, our coreset construction scheme is fairly general and gives
rise to coresets for a wide range of constrained clustering problems. This
leads to improved constant-approximations for these problems in general metrics
and near-linear time -approximations in the Euclidean metric
Improved Approximation and Scalability for Fair Max-Min Diversification
Given an -point metric space where each point belongs to
one of different categories or groups and a set of integers , the fair Max-Min diversification problem is to select
points belonging to category , such that the minimum pairwise
distance between selected points is maximized. The problem was introduced by
Moumoulidou et al. [ICDT 2021] and is motivated by the need to down-sample
large data sets in various applications so that the derived sample achieves a
balance over diversity, i.e., the minimum distance between a pair of selected
points, and fairness, i.e., ensuring enough points of each category are
included. We prove the following results:
1. We first consider general metric spaces. We present a randomized
polynomial time algorithm that returns a factor -approximation to the
diversity but only satisfies the fairness constraints in expectation. Building
upon this result, we present a -approximation that is guaranteed to satisfy
the fairness constraints up to a factor for any constant
. We also present a linear time algorithm returning an
approximation with exact fairness. The best previous result was a
approximation.
2. We then focus on Euclidean metrics. We first show that the problem can be
solved exactly in one dimension. For constant dimensions, categories and any
constant , we present a approximation algorithm that
runs in time where . We can improve the
running time to at the expense of only picking points from category .
Finally, we present algorithms suitable to processing massive data sets
including single-pass data stream algorithms and composable coresets for the
distributed processing.Comment: To appear in ICDT 202
An Empirical Evaluation of k-Means Coresets
Coresets are among the most popular paradigms for summarizing data. In particular, there exist many high performance coresets for clustering problems such as k-means in both theory and practice. Curiously, there exists no work on comparing the quality of available k-means coresets.
In this paper we perform such an evaluation. There currently is no algorithm known to measure the distortion of a candidate coreset. We provide some evidence as to why this might be computationally difficult. To complement this, we propose a benchmark for which we argue that computing coresets is challenging and which also allows us an easy (heuristic) evaluation of coresets. Using this benchmark and real-world data sets, we conduct an exhaustive evaluation of the most commonly used coreset algorithms from theory and practice
Streaming Algorithms for Diversity Maximization with Fairness Constraints
Diversity maximization is a fundamental problem with wide applications in
data summarization, web search, and recommender systems. Given a set of
elements, it asks to select a subset of elements with maximum
\emph{diversity}, as quantified by the dissimilarities among the elements in
. In this paper, we focus on the diversity maximization problem with
fairness constraints in the streaming setting. Specifically, we consider the
max-min diversity objective, which selects a subset that maximizes the
minimum distance (dissimilarity) between any pair of distinct elements within
it. Assuming that the set is partitioned into disjoint groups by some
sensitive attribute, e.g., sex or race, ensuring \emph{fairness} requires that
the selected subset contains elements from each group .
A streaming algorithm should process sequentially in one pass and return a
subset with maximum \emph{diversity} while guaranteeing the fairness
constraint. Although diversity maximization has been extensively studied, the
only known algorithms that can work with the max-min diversity objective and
fairness constraints are very inefficient for data streams. Since diversity
maximization is NP-hard in general, we propose two approximation algorithms for
fair diversity maximization in data streams, the first of which is
-approximate and specific for , where
, and the second of which achieves a
-approximation for an arbitrary . Experimental
results on real-world and synthetic datasets show that both algorithms provide
solutions of comparable quality to the state-of-the-art algorithms while
running several orders of magnitude faster in the streaming setting.Comment: 13 pages, 11 figures; published in ICDE 202
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