There is a more general point that IMO is worth considering. Suppose we're slicing a matrix with row/column names (via traditional methods or via this cool new feature). Should names be carried over to the resulting objects? To be more explicit (quoting from above):

<hansl>
set seed 765545431

matrix M = mnormal(4,3)
cnameset(M, "one two three")
matrix c = M[,"two"]
</hansl>

should the "c" vector be endowed with the column name "two" too? My spontaneous reaction would be "no" (on the grounds of efficiency), but others may disagree.

I think the question of whether names are preserved after indexing/slicing should be separated from the way the slicing is done. I thought that standard (numeric) indexing would preserve the names, but I just checked and it's actually not the case. Maybe because of efficiency as you say. But in any case I think name-indexing should not introduce a special case for this behavior.

thanks

sven