Random Forests for Regression as a Weighted Sum of k-Potential Nearest Neighbors

In this paper, we tackle the problem of random forests for regression expressed as weighted sums of datapoints. We study the theoretical behavior of k-potential nearest neighbors (k-PNNs) under bagging and obtain an upper bound on the weights of a datapoint for random forests with any type of splitting criterion, provided that we use unpruned trees that stop growing only when there are k or less datapoints at their leaves. Moreover, we use the previous bound together with the concept of b-terms (i.e., bootstrap terms) introduced in this paper, to derive the explicit expression of weights for datapoints in a random (k-PNNs) selection setting, a datapoint selection strategy that we also introduce and to build a framework to derive other bagged estimators using a similar procedure. Finally, we derive from our framework the explicit expression of weights of a regression estimate equivalent to a random forest regression estimate with the random splitting criterion and demonstrate its equivalence both theoretically and practically.