Hybrid variations of metaheuristics that include data mining strategies have been utilized to solve a variety of combinatorial optimization problems, with superior and encouraging results. Previous hybrid strategies applied mined patterns to guide the construction of initial solutions, leading to more effective exploration of the solution space. Solving a combinatorial optimization problem is usually a hard task because its solution space grows exponentially with its size. Therefore, problem size reduction is also a useful strategy in this context, especially in the case of large-scale problems. In this paper, we build upon these ideas by presenting an approach named MineReduce, which uses mined patterns to perform problem size reduction. We present an application of MineReduce to improve a heuristic for the heterogeneous fleet vehicle routing problem. The results obtained in computational experiments show that this proposed heuristic demonstrates superior performance compared to the original heuristic and other state-of-the-art heuristics, achieving better solution costs with shorter run times. . This manuscript version is made available under the CC BY-NC-ND 4.0 license. Guerine et al., 2016;Maia et al., 2018;Martins et al., 2018a). Data-mining-hybridized heuristics were able to find solutions of higher quality while spending less computational time when compared to their non-hybridized counterparts and other state-of-the-art heuristics. They applied patterns (found by data mining procedures) to guide the construction of initial solutions.The difficulty in solving a COP is due to the fact that its solution space grows exponentially with its size. Therefore, problem size reduction (PSR) -which consists of reducing the size of a problem instance, then solving the reduced instance and expanding it back -has been found to be a very useful strategy in this context, especially in the case of large-scale problems, since it can significantly reduce the search space of a COP (Gavish & Srikanth, 1986;Fischer & Merz, 2007;Delgadillo et al., 2016).Building upon these ideas, in this paper, we present an approach named MineReduce, which uses mined patterns to perform problem size reduction. Previous methods that also incorporate data mining techniques into metaheuristics, in general, use the mined patterns as a starting point for the construction of initial solutions (Martins et al., 2018b). MineReduce, on the other hand, performs a PSR procedure by removing or merging elements that are in a pattern, finding a solution to the reduced instance, and expanding the solution found, which will be used as the starting point for a local search on the original solution space.In order to validate the MineReduce approach, we have applied it to extend a previous and state-of-theart heuristic for the heterogeneous fleet vehicle routing problem (HFVRP), obtaining significantly better results in terms of both solution quality and computational time.So, the main contribution of this work is twofold: an approach based on the idea of using mi...