Opinion-based optimal group formation

•Identify homogeneous groups of decision-makers based on partial and inconsistent preference information.•Traditional literature focuses on consensus or is unable to handle incomplete information.•Novel MINLP formulation where groups are formed in order to minimize the degree of inconsistency, and group ranking is calculated via Sparse Analytic Hierarchy Process techniques.•The proposed MINLP formulation is non-convex and NP-Hard.•Validated with respect to a case study related to the 2018 Italian Political elections.