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Forests of Randomized Shapelet Trees
Stockholms universitet, Samhällsvetenskapliga fakulteten, Institutionen för data- och systemvetenskap.
Stockholms universitet, Samhällsvetenskapliga fakulteten, Institutionen för data- och systemvetenskap.
Stockholms universitet, Samhällsvetenskapliga fakulteten, Institutionen för data- och systemvetenskap.
2015 (Engelska)Ingår i: Statistical Learning and Data Sciences: Proceedings / [ed] Alexander Gammerman, Vladimir Vovk, Harris Papadopoulos, Springer, 2015, 126-136 s.Konferensbidrag, Publicerat paper (Refereegranskat)
Abstract [en]

Shapelets have recently been proposed for data series classification, due to their ability to capture phase independent and local information. Decision trees based on shapelets have been shown to provide not only interpretable models, but also, in many cases, state-of-the-art predictive performance. Shapelet discovery is however computationally costly, and although several techniques for speeding up the technique have been proposed, the computational cost is still in many cases prohibitive. In this work, an ensemble based method, referred to as Random Shapelet Forest (RSF), is proposed, which builds on the success of the random forest algorithm, and which is shown to have a lower computational complexity than the original shapelet tree learning algorithm. An extensive empirical investigation shows that the algorithm provides competitive predictive performance and that a proposed way of calculating importance scores can be used to successfully identify influential regions.

Ort, förlag, år, upplaga, sidor
Springer, 2015. 126-136 s.
Serie
Lecture Notes in Computer Science, ISSN 0302-9743 ; 9047
Nyckelord [en]
data series classification, shapelets, decision trees, ensemble
Nationell ämneskategori
Systemvetenskap, informationssystem och informatik
Forskningsämne
data- och systemvetenskap
Identifikatorer
URN: urn:nbn:se:su:diva-122820DOI: 10.1007/978-3-319-17091-6_8ISBN: 978-3-319-17091-6 (tryckt)OAI: oai:DiVA.org:su-122820DiVA: diva2:868623
Konferens
Third International Symposium, SLDS 2015, Egham, UK, April 20-23, 2015
Tillgänglig från: 2015-11-11 Skapad: 2015-11-10 Senast uppdaterad: 2017-04-28Bibliografiskt granskad
Ingår i avhandling
1. Order in the random forest
Öppna denna publikation i ny flik eller fönster >>Order in the random forest
2017 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

In many domains, repeated measurements are systematically collected to obtain the characteristics of objects or situations that evolve over time or other logical orderings. Although the classification of such data series shares many similarities with traditional multidimensional classification, inducing accurate machine learning models using traditional algorithms are typically infeasible since the order of the values must be considered.

In this thesis, the challenges related to inducing predictive models from data series using a class of algorithms known as random forests are studied for the purpose of efficiently and effectively classifying (i) univariate, (ii) multivariate and (iii) heterogeneous data series either directly in their sequential form or indirectly as transformed to sparse and high-dimensional representations. In the thesis, methods are developed to address the challenges of (a) handling sparse and high-dimensional data, (b) data series classification and (c) early time series classification using random forests. The proposed algorithms are empirically evaluated in large-scale experiments and practically evaluated in the context of detecting adverse drug events.

In the first part of the thesis, it is demonstrated that minor modifications to the random forest algorithm and the use of a random projection technique can improve the effectiveness of random forests when faced with discrete data series projected to sparse and high-dimensional representations. In the second part of the thesis, an algorithm for inducing random forests directly from univariate, multivariate and heterogeneous data series using phase-independent patterns is introduced and shown to be highly effective in terms of both computational and predictive performance. Then, leveraging the notion of phase-independent patterns, the random forest is extended to allow for early classification of time series and is shown to perform favorably when compared to alternatives. The conclusions of the thesis not only reaffirm the empirical effectiveness of random forests for traditional multidimensional data but also indicate that the random forest framework can, with success, be extended to sequential data representations.

Ort, förlag, år, upplaga, sidor
Stockholm: Department of Computer and Systems Sciences, Stockholm University, 2017. 76 s.
Serie
Report Series / Department of Computer & Systems Sciences, ISSN 1101-8526 ; 17-004
Nyckelord
Machine learning, random forest, ensemble, time series, data series, sequential data, sparse data, high-dimensional data
Nationell ämneskategori
Data- och informationsvetenskap
Forskningsämne
data- och systemvetenskap
Identifikatorer
urn:nbn:se:su:diva-142052 (URN)978-91-7649-827-9 (ISBN)978-91-7649-828-6 (ISBN)
Disputation
2017-06-08, L30, NOD-huset, Borgarfjordsgatan 12, Stockholm, 13:00 (Engelska)
Opponent
Handledare
Forskningsfinansiär
Stiftelsen för strategisk forskning (SSF), IIS11-0053
Tillgänglig från: 2017-05-16 Skapad: 2017-04-24 Senast uppdaterad: 2017-05-15Bibliografiskt granskad

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Av författaren/redaktören
Karlsson, IsakPapapetrou, PanagiotisBoström, Henrik
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Institutionen för data- och systemvetenskap
Systemvetenskap, informationssystem och informatik

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