kNN-IS: an iterative spark-based design of the k-nearest neighbors classifier for big data

The k-Nearest Neighbors classifier is a simple yet effective widely renowned method in data mining. The actual application of this model in the big data domain is not feasible due to time and memory restrictions. Several distributed alternatives based on MapReduce have been proposed to enable this method to handle large-scale data. However, their performance can be further improved with new designs that fit with newly arising technologies. In this work we provide a new solution to perform an exact k-nearest neighbor classification based on Spark. We take advantage of its in-memory operations to classify big amounts of unseen cases against a big training dataset. The map phase computes the k-nearest neighbors in different training data splits. Afterwards, multiple reducers process the definitive neighbors from the list obtained in the map phase. The key point of this proposal lies on the management of the test set, keeping it in memory when possible. Otherwise, it is split into a minimum number of pieces, applying a MapReduce per chunk, using the caching skills of Spark to reuse the previously partitioned training set. In our experiments we study the differences between Hadoop and Spark implementations with datasets up to 11 million instances, showing the scaling-up capabilities of the proposed approach. As a result of this work an open-source Spark package is available

From Big data to Smart Data with the K-Nearest Neighbours algorithm

The k-nearest neighbours algorithm is one of the most widely used data mining models because of its simplicity and accurate results. However, when it comes to deal with big datasets, with potentially noisy and missing information, this technique becomes ineffective and inefficient. Due to its drawbacks to tackle large amounts of imperfect data, plenty of research has aimed at improving this algorithm by means of data preprocessing techniques. These weaknesses have turned out as strengths and the k-nearest neighbours rule has become a core model to actually detect and correct imperfect data, eliminating noisy and redundant data, as well as correcting missing values. In this work, we delve into the role of the k nearest neighbour algorithm to come up with smart data from big datasets. We analyse how this model is affected by the big data problem, but at the same time, how it can be used to transform raw data into useful data. Concretely, we discuss the benefits of recent big data technologies (Hadoop and Spark) to enable this model to address large amounts of data, as well as the usefulness of prototype reduction and missing values imputation techniques based on it. As a result, guidelines on the use of the k-nearest neighbour to obtain Smart data are provided and new potential research trends are drawn

Evolutionary undersampling for extremely imbalanced big data classification under apache spark

The classification of datasets with a skewed class distribution is an important problem in data mining. Evolutionary undersampling of the majority class has proved to be a successful approach to tackle this issue. Such a challenging task may become even more difficult when the number of the majority class examples is very big. In this scenario, the use of the evolutionary model becomes unpractical due to the memory and time constrictions. Divide-and-conquer approaches based on the MapReduce paradigm have already been proposed to handle this type of problems by dividing data into multiple subsets. However, in extremely imbalanced cases, these models may suffer from a lack of density from the minority class in the subsets considered. Aiming at addressing this problem, in this contribution we provide a new big data scheme based on the new emerging technology Apache Spark to tackle highly imbalanced datasets. We take advantage of its in-memory operations to diminish the effect of the small sample size. The key point of this proposal lies in the independent management of majority and minority class examples, allowing us to keep a higher number of minority class examples in each subset. In our experiments, we analyze the proposed model with several data sets with up to 17 million instances. The results show the goodness of this evolutionary undersampling model for extremely imbalanced big data classification

Fast and Scalable Approaches to Accelerate the Fuzzy k Nearest Neighbors Classifier for Big Data

One of the best-known and most effective methods in supervised classification is the k nearest neighbors algorithm (kNN). Several approaches have been proposed to improve its accuracy, where fuzzy approaches prove to be among the most successful, highlighting the classical Fuzzy k nearest neighbors (FkNN). However, these traditional algorithms fail to tackle the large amounts of data that are available today. There are multiple alternatives to enable kNN classification in big datasets, spotlighting the approximate version of kNN called Hybrid Spill Tree. Nevertheless, the existing proposals of FkNN for big data problems are not fully scalable, because a high computational load is required to obtain the same behavior as the original FkNN algorithm. This work proposes Global Approximate Hybrid Spill Tree FkNN and Local Hybrid Spill Tree FkNN, two approximate approaches that speed up runtime without losing quality in the classification process. The experimentation compares various FkNN approaches for big data with datasets of up to 11 million instances. The results show an improvement in runtime and accuracy over literature algorithms

From Big data to Smart Data with the K-Nearest Neighbours algorithm

The k-nearest neighbours algorithm is one of the most widely used data mining models because of its simplicity and accurate results. However, when it comes to deal with big datasets, with potentially noisy and missing information, this technique becomes ineffective and inefficient. Due to its drawbacks to tackle large amounts of imperfect data, plenty of research has aimed at improving this algorithm by means of data preprocessing techniques. These weaknesses have turned out as strengths and the k-nearest neighbours rule has become a core model to actually detect and correct imperfect data, eliminating noisy and redundant data, as well as correcting missing values. In this work, we delve into the role of the k nearest neighbour algorithm to come up with smart data from big datasets. We analyse how this model is affected by the big data problem, but at the same time, how it can be used to transform raw data into useful data. Concretely, we discuss the benefits of recent big data technologies (Hadoop and Spark) to enable this model to address large amounts of data, as well as the usefulness of prototype reduction and missing values imputation techniques based on it. As a result, guidelines on the use of the k-nearest neighbour to obtain Smart data are provided and new potential research trends are drawn

Exact fuzzy k-Nearest neighbor classification for big datasets

The k-Nearest Neighbors (kNN) classifier is one of the most effective methods in supervised learning problems. It classifies unseen cases comparing their similarity with the training data. Nevertheless, it gives to each labeled sample the same importance to classify. There are several approaches to enhance its precision, with the Fuzzy k Nearest Neighbors (FuzzykNN) classifier being among the most successful ones. FuzzykNN computes a fuzzy degree of membership of each instance to the classes of the problem. As a result, it generates smoother borders between classes. Apart from the existing kNN approach to handle big datasets, there is not a fuzzy variant to manage that volume of data. Nevertheless, calculating this class membership adds an extra computational cost becoming even less scalable to tackle large datasets because of memory needs and high runtime. In this work, we present an exact and distributed approach to run the Fuzzy-kNN classifier on big datasets based on Spark, which provides the same precision than the original algorithm. It presents two separately stages. The first stage transforms the training set adding the class membership degrees. The second stage classifies with the kNN algorithm the test set using the class membership computed previously. In our experiments, we study the scaling-up capabilities of the proposed approach with datasets up to 11 million instances, showing promising results

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Peer reviewe

Evolutionary undersampling for extremely imbalanced big data classification under apache spark

The classification of datasets with a skewed class distribution is an important problem in data mining. Evolutionary undersampling of the majority class has proved to be a successful approach to tackle this issue. Such a challenging task may become even more difficult when the number of the majority class examples is very big. In this scenario, the use of the evolutionary model becomes unpractical due to the memory and time constrictions. Divide-and-conquer approaches based on the MapReduce paradigm have already been proposed to handle this type of problems by dividing data into multiple subsets. However, in extremely imbalanced cases, these models may suffer from a lack of density from the minority class in the subsets considered. Aiming at addressing this problem, in this contribution we provide a new big data scheme based on the new emerging technology Apache Spark to tackle highly imbalanced datasets. We take advantage of its in-memory operations to diminish the effect of the small sample size. The key point of this proposal lies in the independent management of majority and minority class examples, allowing us to keep a higher number of minority class examples in each subset. In our experiments, we analyze the proposed model with several data sets with up to 17 million instances. The results show the goodness of this evolutionary undersampling model for extremely imbalanced big data classification