Two questions about matrix indexing:
Is is correct that V <- V[lower.tri(V, diag=TRUE)] returns the lower
triangular of matrix V, that is: all elements above diagonal are set to zero? I
understand that the triangle of matrix elements of V for which lower.tri is
TRUE are returned while the others (above diagonal) are set to zero (or NA ???).
If D and B are vectors of logicals,
what does V contain after V <- v[D, B, drop=FALSE] ?
I guess that elements are returned if both indexes D and B are TRUE, but I'm
not really convinced... (And again, what about the other elements?)
These are probably tutorial questions, but I'm still not sure after reading "R
Language Definition (draft): Evaluation of expressions" and applicable sections
of "The R Reference Manual". Thanx!
W. Beldman