Many thanks to everyone for the ideas and links! I'll study them carefully
and when I finish my package I'll submit it to CRAN and post the details
here.

Now I see that the "[1]" expression was not such a good idea (I wanted an
analogy with the "deep" subscript operator "[[ ]]" for lists). The solutions
suggested by Gabor Grothendieck and Tony Plate seem more intuitive.

I wonder why R itself does not distinguish between "1" and "1:1" (e.g.,
using the dim attribute) to decide which dimensions should be dropped.

Many thanks again,
Regards,

Maciej.

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