“…The popular lasso estimator (least absolute shrinkage and selection operator, Tibshirani ()), based on penalized least squares, has been extended in the last years to nonparametric regression, as in Bunea, Tsybakov, and Wegkamp (, ,), Bunea (), Bickel, Ritov, and Tsybakov (), van de Geer (), and Bühlmann and van de Geer (), among others. Arribas‐Gil et al () proposed to reconstruct a sparse approximation of f with linear combinations of elements of a given set of functions , called dictionary: where . In practice, for the nonparametric regression problem, the dictionary can be a collection of basis functions from different bases (splines with fixed knots, wavelets, Fourier, etc.).…”