1. A computer program product, comprising: a non-transitory computer-readable storage medium having computer-readable program code embodied therewith, the computer-readable program code comprising: computer-readable program code configured to generate, using a first map operation for each of a plurality of data sources, a validation sample from the respective data source and a base model by applying a specified learning technique to data in the respective data source that was not included in any sample; computer-readable program code configured to merge, using a first reduce operation, a portion of the validation samples that does not exceed a predefined maximum size for the plurality of data sources into a global validation dataset; computer-readable program code configured to score, using a second map operation, each base model by computing a score for each record in the global validation dataset; computer-readable program code configured to determine, using the second map operation for each of the plurality of data sources, an accuracy value for each base model based on the global validation dataset by comparing each computed score against a target value in the global validation dataset, wherein each base model is compared using data from a data source other than the data source from which the base model was generated, wherein the computed score for a record is correct when the computed score matches a corresponding target value, and wherein an accuracy value of each base model is determined as a percentage of correct scores; and computer-readable program code configured to generate, using a second reduce operation, an ensemble model that includes a subset of the base models that are selected based on the determined accuracy values and that includes one or more rules for combining predictions of the subset of the base models.