Adaptive ensemble of classifiers with regularization for imbalanced data classification

The dynamic ensemble selection of classifiers is an effective approach for processing label-imbalanced data classifications. However, such a technique is prone to overfitting, owing to the lack of regularization methods and the dependence on local geometry of data. In this study, focusing on binary imbalanced data classification, a novel dynamic ensemble method, namely adaptive ensemble of classifiers with regularization (AER), is proposed, to overcome the stated limitations. The method solves the overfitting problem through a new perspective of implicit regularization. Specifically, it leverages the properties of stochastic gradient descent to obtain the solution with the minimum norm, thereby achieving regularization; furthermore, it interpolates the ensemble weights by exploiting the global geometry of data to further prevent overfitting. According to our theoretical proofs, the seemingly complicated AER paradigm, in addition to its regularization capabilities, can actually reduce the asymptotic time and memory complexities of several other algorithms. We evaluate the proposed AER method on seven benchmark imbalanced datasets from the UCI machine learning repository and one artificially generated GMM-based dataset with five variations. The results show that the proposed algorithm outperforms the major existing algorithms based on multiple metrics in most cases, and two hypothesis tests (McNemar’s and Wilcoxon tests) verify the statistical significance further. In addition, the proposed method has other preferred properties such as special advantages in dealing with highly imbalanced data, and it pioneers the researches on regularization for dynamic ensemble methods.     

A novel ensemble of classifiers for microarray data classification

Micorarray data are often extremely asymmetric in dimensionality, such as thousands or even tens of thousands of genes and a few hundreds of samples. Such extreme asymmetry between the dimensionality of genes and samples presents several challenges to conventional clustering and classification methods. In this paper, a novel ensemble method is proposed. Firstly, in order to extract useful features and reduce dimensionality, different feature selection methods such as correlation analysis, Fisher-ratio is used to form different feature subsets. Then a pool of candidate base classifiers is generated to learn the subsets which are re-sampling from the different feature subsets with PSO (Particle Swarm Optimization) algorithm. At last, appropriate classifiers are selected to construct the classification committee using EDAs (Estimation of Distribution Algorithms). Experiments show that the proposed method produces the best recognition rates on four benchmark databases.     

结合X-means聚类的自适应随机子空间组合分类算法

针对大规模数据的分类准确率低且效率下降的问题,提出一种结合X-means聚类的自适应随机子空间组合分类算法。首先使用X-means聚类方法,保持原有数据结构的同时,把复杂的数据空间自动分解为多个样本子空间进行分治学习;而自适应随机子空间组合分类器,提升了基分类器的差异性并自动确定基分类器数量,提升了组合分类器的鲁棒性及分类准确性。该算法在人工和UCI数据集上进行了测试,并与传统单分类和组合分类算法进行了比较。实验结果表明,对于大规模数据集,该方法具有更好的分类精度和健壮性,并提升了整体算法的效率。     

An ensemble of filters and classifiers for microarray data classification

In this paper a new framework for feature selection consisting of an ensemble of filters and classifiers is described. Five filters, based on different metrics, were employed. Each filter selects a different subset of features which is used to train and to test a specific classifier. The outputs of these five classifiers are combined by simple voting. In this study three well-known classifiers were employed for the classification task: C4.5, naive-Bayes and IB1. The rationale of the ensemble is to reduce the variability of the features selected by filters in different classification domains. Its adequacy was demonstrated by employing 10 microarray data sets.     

Temporal data classification using linear classifiers

Data classification is usually based on measurements recorded at the same time. This paper considers temporal data classification where the input is a temporal database that describes measurements over a period of time in history while the predicted class is expected to occur in the future. We describe a new temporal classification method that improves the accuracy of standard classification methods. The benefits of the method are tested on weather forecasting using the meteorological database from the Texas Commission on Environmental Quality and on influenza using the Google Flu Trends database.     

Recognition of driving postures by combined features and random subspace ensemble of multilayer perceptron classifiers

Human-centric driver assistance systems with integrated sensing, processing and networking aim to find solutions for traffic accidents and other relevant issues. The key technology for developing such a system is the capability of automatically understanding and characterizing driver behaviors. This paper proposes a novel driving posture recognition approach, which consists of an efficient combined feature extraction and a random subspace ensemble of multilayer perceptron classifiers. A Southeast University Driving Posture Database (SEU-DP Database) has been created for training and testing the proposed approach. The data set contains driver images of (1) grasping the steering wheel, (2) operating the shift lever, (3) eating a cake and (4) talking on a cellular phone. Combining spatial scale features and histogram-based features, holdout and cross-validation experiments on driving posture classification are conducted, comparatively. The experimental results indicate that the proposed combined feature extraction approach with random subspace ensemble of multilayer perceptron classifiers outperforms the two individual feature extraction approaches. The experiments also suggest that talking on a cellular phone is the most difficult posture in classification among the four predefined postures. Using the proposed approach, the classification accuracy on talking on a cellular phone is over 89 % in both holdout and cross-validation experiments. These results show the effectiveness of the proposed combined feature extraction approach and random subspace ensemble of multilayer perceptron classifiers in automatically understanding and characterizing driver behaviors toward human-centric driver assistance systems.

     

Erratum to: Recognition of driving postures by combined features and random subspace ensemble of multilayer perceptron classifiers

Neural Computing and Applications -     

三种用于垃圾网页检测的随机欠采样集成分类器

针对垃圾网页检测过程中轻微的不平衡分类问题,提出三种随机欠采样集成分类器算法,分别为一次不放回随机欠采样（RUS-once）、多次不放回随机欠采样（RUS-multiple）和有放回随机欠采样（RUS-replacement）算法。首先使用其中一种随机欠采样技术将训练样本集转换成平衡样本集,然后对每个平衡样本集使用分类回归树（CART）分类器算法进行分类,最后采用简单投票法构建集成分类器对测试样本进行分类。实验表明,三种随机欠采样集成分类器均取得了良好的分类效果,其中RUS-multiple和RUS-replacement比RUS-once的分类效果更好。与CART及其Bagging和Adaboost集成分类器相比,在WEBSPAM UK-2006数据集上,RUS-multiple和RUS-replacement方法的AUC指标值提高了10%左右,在WEBSPAM UK-2007数据集上,提高了25%左右;与其他最优研究结果相比,RUS-multiple和RUS-replacement方法在AUC指标上能达到最优分类结果。     

Multilabel classification using heterogeneous ensemble of multi-label classifiers

Multilabel classification is a challenging research problem in which each instance may belong to more than one class. Recently, a considerable amount of research has been concerned with the development of “good” multi-label learning methods. Despite the extensive research effort, many scientific challenges posed by e.g. highly imbalanced training sets and correlation among labels remain to be addressed. The aim of this paper is to use a heterogeneous ensemble of multi-label learners to simultaneously tackle both the sample imbalance and label correlation problems. This is different from the existing work in the sense that we are proposing to combine state-of-the-art multi-label methods by ensemble techniques instead of focusing on ensemble techniques within a multi-label learner. The proposed ensemble approach (EML) is applied to six publicly available multi-label data sets from various domains including computer vision, biology and text using several evaluation criteria. We validate the advocated approach experimentally and demonstrate that it yields significant performance gains when compared with state-of-the art multi-label methods.     

Improving handwriting based gender classification using ensemble classifiers

This paper presents a system to predict gender of individuals from offline handwriting samples. The technique relies on extracting a set of textural features from handwriting samples of male and female writers and training multiple classifiers to learn to discriminate between the two gender classes. The features include local binary patterns (LBP), histogram of oriented gradients (HOG), statistics computed from gray-level co-occurrence matrices (GLCM) and features extracted through segmentation-based fractal texture analysis (SFTA). For classification, we employ artificial neural networks (ANN), support vector machine (SVM), nearest neighbor classifier (NN), decision trees (DT) and random forests (RF). Classifiers are then combined using bagging, voting and stacking techniques to enhance the overall system performance. The realized classification rates are significantly better than those of the state-of-the-art systems on this problem validating the ideas put forward in this study.     

Probabilistic semi-supervised random subspace sparse representation for classification

In this paper, we present a novel approach for classification named Probabilistic Semi-supervised Random Subspace Sparse Representation (P-RSSR). In many random subspaces based methods, all features have the same probability to be selected to compose the random subspace. However, in the real world, especially in images, some regions or features are important for classification and some are not. In the proposed P-RSSR, firstly, we calculate the distribution probability of the image and determine which feature is selected to compose the random subspace. Then, we use Sparse Representation (SR) to construct graphs to characterize the distribution of samples in random subspaces, and train classifiers under the framework of Manifold Regularization (MR) in these random subspaces. Finally, we fuse the results in all random subspaces and obtain the classified results through majority vote. Experimental results on face image datasets have demonstrated the effectiveness of the proposed P-RSSR.     

Decoding visual brain states from fMRI using an ensemble of classifiers

Decoding perceptual or cognitive states based on brain activity measured using functional magnetic resonance imaging (fMRI) can be achieved using machine learning algorithms to train classifiers of specific stimuli. However, the high dimensionality and intrinsically low signal to noise ratio (SNR) of fMRI data poses great challenges to such techniques. The problem is aggravated in the case of multiple subject experiments because of the high inter-subject variability in brain function. To address these difficulties, the majority of current approaches uses a single classifier. Since, in many cases, different stimuli activate different brain areas, it makes sense to use a set of classifiers each specialized in a different stimulus. Therefore, we propose in this paper using an ensemble of classifiers for decoding fMRI data. Each classifier in the ensemble has a favorite class or stimulus and uses an optimized feature set for that particular stimulus. The output for each individual stimulus is therefore obtained from the corresponding classifier and the final classification is achieved by simply selecting the best score. The method was applied to three empirical fMRI datasets from multiple subjects performing visual tasks with four classes of stimuli. Ensembles of GNB and k-NN base classifiers were tested. The ensemble of classifiers systematically outperformed a single classifier for the two most challenging datasets. In the remaining dataset, a ceiling effect was observed which probably precluded a clear distinction between the two classification approaches. Our results may be explained by the fact that different visual stimuli elicit specific patterns of brain activation and indicate that an ensemble of classifiers provides an advantageous alternative to commonly used single classifiers, particularly when decoding stimuli associated with specific brain areas.     

基于自适应随机森林的数据流分类算法

自适应随机森林分类器在每个基础分类器上分别设置了警告探测器和漂移探测器,实例训练时常常会同时触发多个警告探测器,引起多棵背景树同步训练,使得运行所需的内存大、时间长。针对此问题,提出了一种改进的自适应随机森林集成分类算法,将概念漂移探测器设置在集成学习器端,移除各基础树端的漂移探测器,并根据集成器预测准确率确定需要训练的背景树的数量。用改进后的算法对较平衡的数据流进行分类,在保证分类性能的前提下,与改进前的算法相比,运行时间有所降低,消耗内存有所减少,能更快适应数据流中出现的概念漂移。     

新型含噪数据流集成分类的算法

针对数据流中概念漂移和噪声问题,提出一种新型的增量式学习的数据流集成分类算法。首先,引入噪声过滤机制过滤噪声;然后,引入假设检验方法对概念漂移进行检测,以增量式C4.5决策树为基分类器构建加权集成模型;最后,实现增量式学习实例并随之动态更新分类模型。实验结果表明,该集成分类器对概念漂移的检测精度达到95%~97%,对数据流抗噪性保持在90%以上。该算法分类精度较高,且在检测概念漂移的准确性和抗噪性方面有较好的表现。     

数据流中概念漂移检测的集成分类器设计

提出了一种称为ICEA(incremental classification ensemble algorithm)的数据流挖掘算法.它利用集成分类器综合技术,实现了数据流中概念漂移的增量式检测和挖掘.实验结果表明,ICEA在处理数据流的快速概念漂移上表现出很高的精确度和较好的时间效率.     

On learning dual classifiers for better data classification

Instance selection aims at filtering out noisy data (or outliers) from a given training set, which not only reduces the need for storage space, but can also ensure that the classifier trained by the reduced set provides similar or better performance than the baseline classifier trained by the original set. However, since there are numerous instance selection algorithms, there is no concrete winner that is the best for various problem domain datasets. In other words, the instance selection performance is algorithm and dataset dependent. One main reason for this is because it is very hard to define what the outliers are over different datasets. It should be noted that, using a specific instance selection algorithm, over-selection may occur by filtering out too many ‘good’ data samples, which leads to the classifier providing worse performance than the baseline. In this paper, we introduce a dual classification (DuC) approach, which aims to deal with the potential drawback of over-selection. Specifically, performing instance selection over a given training set, two classifiers are trained using both a ‘good’ and ‘noisy’ sets respectively identified by the instance selection algorithm. Then, a test sample is used to compare the similarities between the data in the good and noisy sets. This comparison guides the input of the test sample to one of the two classifiers. The experiments are conducted using 50 small scale and 4 large scale datasets and the results demonstrate the superior performance of the proposed DuC approach over the baseline instance selection approach.     

The random electrode selection ensemble for EEG signal classification

Pattern classification methods are a crucial direction in the current study of brain–computer interface (BCI) technology. A simple yet effective ensemble approach for electroencephalogram (EEG) signal classification named the random electrode selection ensemble (RESE) is developed, which aims to surmount the instability demerit of the Fisher discriminant feature extraction for BCI applications. Through the random selection of recording electrodes answering for the physiological background of user-intended mental activities, multiple individual classifiers are constructed. In a feature subspace determined by a couple of randomly selected electrodes, principal component analysis (PCA) is first used to carry out dimensionality reduction. Successively Fisher discriminant is adopted for feature extraction, and a Bayesian classifier with a Gaussian mixture model (GMM) approximating the feature distribution is trained. For a test sample the outputs from all the Bayesian classifiers are combined to give the final prediction for its label. Theoretical analysis and classification experiments with real EEG signals indicate that the RESE approach is both effective and efficient.     

The random boosting ensemble classifier for land-use image classification

This paper presents a random boosting ensemble (RBE) classifier for remote sensing image classification, which introduces the random projection feature selection and bootstrap methods to obtain base classifiers for classifier ensemble. The RBE method is built based on an improved boosting framework, which is quite efficient for the few-shot problem due to the bootstrap in use. In RBE, kernel extreme machine (KELM) is applied to design base classifiers, which actually make RBE quite efficient due to feature reduction. The experimental results on the remote scene image classification demonstrate that RBE can effectively improve the classification performance, and resulting into a better generalization ability on the 21-class land-use dataset and the India pine satellite scene dataset.

     

Semi-supervised classification based on random subspace dimensionality reduction

Graph structure is vital to graph based semi-supervised learning. However, the problem of constructing a graph that reflects the underlying data distribution has been seldom investigated in semi-supervised learning, especially for high dimensional data. In this paper, we focus on graph construction for semi-supervised learning and propose a novel method called Semi-Supervised Classification based on Random Subspace Dimensionality Reduction, SSC-RSDR in short. Different from traditional methods that perform graph-based dimensionality reduction and classification in the original space, SSC-RSDR performs these tasks in subspaces. More specifically, SSC-RSDR generates several random subspaces of the original space and applies graph-based semi-supervised dimensionality reduction in these random subspaces. It then constructs graphs in these processed random subspaces and trains semi-supervised classifiers on the graphs. Finally, it combines the resulting base classifiers into an ensemble classifier. Experimental results on face recognition tasks demonstrate that SSC-RSDR not only has superior recognition performance with respect to competitive methods, but also is robust against a wide range of values of input parameters.