Re: [Rd] Associative array?

From: Ben <misc7_at_emerose.org>
Date: Thu, 11 Mar 2010 18:09:09 -0600

> 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 array.

> 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

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