PAC-learning usually aims to compute a small subset ($varepsilon$-sample/net) from $n$ items, that provably approximates a given loss function for every query (model, classifier, hypothesis) from a given set of queries, up to an additive error $varepsilonin(0,1)$. Coresets generalize this idea to support multiplicative error $1pmvarepsilon$. Inspired by smoothed analysis, we suggest a natural generalization: approximate the emph{average} (instead of the worst-case) error over the queries, in the hope of getting smaller subsets. The dependency between errors of different queries implies that we may no longer apply the Chernoff-Hoeffding inequality for a fixed query, and then use the VC-dimension or union bound. This paper provides deterministic and randomized algorithms for computing such coresets and $varepsilon$-samples of size independent of $n$, for any finite set of queries and loss function. Example applications include new and improved coreset constructions for e.g. streaming vector summarization [ICML17] and $k$-PCA [NIPS16]. Experimental results with open source code are provided.
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