Types of cost in inductive concept learning

Inductive concept learning is the task of learning to assign cases to a discrete set of classes. In real-world applications of concept learning, there are many different types of cost involved. The majority of the machine learning literature ignores all types of cost (unless accuracy is interpreted as a type of cost measure). A few papers have investigated the cost of misclassification errors. Very few papers have examined the many other types of cost. In this paper, we attempt to create a taxonomy of the different types of cost that are involved in inductive concept learning. This taxonomy may help to organize the literature on cost-sensitive learning. We hope that it will inspire researchers to investigate all types of cost in inductive concept learning in more depth

Mining Top-K Frequent Itemsets Through Progressive Sampling

We study the use of sampling for efficiently mining the top-K frequent itemsets of cardinality at most w. To this purpose, we define an approximation to the top-K frequent itemsets to be a family of itemsets which includes (resp., excludes) all very frequent (resp., very infrequent) itemsets, together with an estimate of these itemsets' frequencies with a bounded error. Our first result is an upper bound on the sample size which guarantees that the top-K frequent itemsets mined from a random sample of that size approximate the actual top-K frequent itemsets, with probability larger than a specified value. We show that the upper bound is asymptotically tight when w is constant. Our main algorithmic contribution is a progressive sampling approach, combined with suitable stopping conditions, which on appropriate inputs is able to extract approximate top-K frequent itemsets from samples whose sizes are smaller than the general upper bound. In order to test the stopping conditions, this approach maintains the frequency of all itemsets encountered, which is practical only for small w. However, we show how this problem can be mitigated by using a variation of Bloom filters. A number of experiments conducted on both synthetic and real bench- mark datasets show that using samples substantially smaller than the original dataset (i.e., of size defined by the upper bound or reached through the progressive sampling approach) enable to approximate the actual top-K frequent itemsets with accuracy much higher than what analytically proved.Comment: 16 pages, 2 figures, accepted for presentation at ECML PKDD 2010 and publication in the ECML PKDD 2010 special issue of the Data Mining and Knowledge Discovery journa

Échantillonnage progressif guidé pour stabiliser la courbe d'apprentissage

National audienceL'un des enjeux de l'apprentissage artificiel est de pouvoir fonctionner avec des volumes de données toujours plus grands. Bien qu'il soit généralement admis que plus un ensemble d'apprentissage est large et plus les résultats sont performants, il existe des limites à la masse d'informations qu'un algorithme d'apprentissage peut manipuler. Pour résoudre ce problème, nous proposons d'améliorer la méthode d'échantillonnage progressif en guidant la construction d'un ensemble d'apprentissage réduit à partir d'un large ensemble de données. L'apprentissage à partir de l'ensemble réduit doit conduire à des performances similaires à l'apprentissage effectué avec l'ensemble complet. Le guidage de l'échantillonnage s'appuie sur une connaissance a priori qui accélère la convergence de l'algorithme. Cette approche présente trois avantages : 1) l'ensemble d'apprentissage réduit est composé des cas les plus représentatifs de l'ensemble complet; 2) la courbe d'apprentissage est stabilisée; 3) la détection de convergence est accélérée. L'application de cette méthode à des données classiques et à des données provenant d'unités de soins intensifs révèle qu'il est possible de réduire de façon significative un ensemble d'apprentissage sans diminuer la performance de l'apprentissage