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Map-like helper functions #3339
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@florence-bockting this may be a nice stepping stone beyond modifying the existing Laplace code if you'd like to get involved more in the C++ development after your first PR is done!
Reacted by Florence BocktingI think this is a very cool idea. I think we would want something that has similar mechanics to
filter_map(...), but has specific rules for operating on particular containers.To make @WardBrian 's a little more concrete I think we would want these signatures
// General map on elements of `T[i]` // Calls f(t[i]) template <typename F, typename T> auto map(F&& f, T&& t); /** * Iterate over N items with identical dimensions * f(args<0>[i], args<1>[i], ..., args<j>[i]); */ template <typename F, typename... Types> auto mapN(F&& f, Types&&... args);
And then we would have something similar for
row_mapandrow_mapNalong withcol_mapandcol_mapN// General map on rows of `T` // Calls f(t.row(i)) template <typename F, typename T> auto row_map(F&& f, T&& t); /** * Iterate over the rows of N items with identical dimensions * f(args<0>.row(i), args<1>.row(i), ..., args<j>.row(i)); */ template <typename F, typename... Types> auto row_mapN(F&& f, Types&&... args);
The map-family of functions would make writing certain kinds of models easier. Because we lack closures (#2197) it would make sense to make them variadic, so a basic
mapwould have the signaturemap(f, T, ...)which would callf(T[1], ...),f(T[2], ...)etc.A few variants of this would be useful, such as
map2which maps over two containers of the same size,and specialized
row_map/column_mapfor matrices, which would allow e.g.(suggested by @bob-carpenter)