  Many next-to-leading order QCD predictions are available through Monte Carlo
(MC) simulations. Usually, multiple CPU hours are needed to calculate
predictions at a required precision, which is unfeasible for global PDF
analyses. This problem is solved by a process known as gridding: The values of
the hard-scattering cross-section are calculated only once with the MC program,
and then interpolated and stored in look-up tables (grids) of the kinematical
variables. To obtain the physical predictions, they are convolved with the PDFs
(e.g. during the fitting stage in a PDF global analysis), which takes a tiny
fraction of the time needed to calculate the MC results. This is possible with
PineAPPL, a library tackling the aforementioned process of grid creation and
convolution. In this work, we use PineAPPL to grid the predictions for open
heavy-flavor production in the general-mass variable-flavor-number scheme
(GM-VFNS). In the GM-VFNS, the differential cross-section interpolates between
the fixed-flavor-number scheme (FFNS) and the zero-mass variable-flavor-number
scheme (ZM-VFNS). These are each only valid in different kinematical regions,
in which the GM-VFNS cross-section reproduces the FFNS and ZM-VFNS as the
limiting cases of high energies and small masses, respectively. Better than
permille agreement is achieved between the grids and the MC predictions, while
at the same time not substantially increasing the time of the MC calculations.
