[Rd] Associative array?

Ben misc7 at emerose.org
Fri Mar 12 01:09:09 CET 2010

> lists are generic vectors with names so lookup is O(n). Environments  
> in R are true hash tables for that purpose:

Ahh, thanks for the information!  A function I wrote before indexing
on a data frame was slower than I expected, and now I know why.

> I don't quite understand - characters are (after raw vectors) the
> most expressive data type, so I'm not quite sure why that would be a
> limitation .. You can cast anything (but raw vector with nulls) into
> to a character.

It's no big problem, it's just that if the solution is to convert to
character type, then there are some implementation details to worry
about.  For instance, I assume that as.character(x) is a reversible
1-1 mapping if x is an integer (and not NA or NULL, etc).  But
apparently that isn't exactly true for floats, and it would get more
complicated for other data types.  So that's why I said it would not
be elegant, but that is a very subjective statement.

On a deeper level, it seems counterintuitive to me that indexing in R
is O(n).  Futhermore, associative arrays are a fundamental data type,
so I think it's weird that I can read the R tutorial, the R language
definition, and even the manual page for new.env() and still not have
enough information to build a decent one.  So IMHO things would be
better if R had a built-in easy-to-use general purpose associative

> I don't see a problem thus I'm not surprised it didn't come up
> ;). But maybe I'm just missing your point ...

Nope, this has come up before---I think R and I are just on different
wavelengths.  Various things that I think are a problem with R are
apparently not, and it's fine the way it is.

Anyway, sorry for getting off topic ;-) You posted everything I need to know and I really appreciate your help.

Ben Escoto

More information about the R-devel mailing list