[R] how to do java-like hashtables in R, R from a java programmer's p onit of view

Peter Dalgaard BSA p.dalgaard at biostat.ku.dk
Wed Apr 25 22:06:02 CEST 2001

Chris Marshall <chrism at norcomnetworks.com> writes:

> In R, you might proceed as follows to build such a table.  Say x is some
> list object.  Say you have a loop that is reading key/value pairs into the
> variables "key" and "value" one after another.
> Putting the pair in the table is as simple as:
> x[[key]] <- value
> Later, retrieving a value from a key would be:
> x[[key]]

Actually, the linear structure of a list in R makes this rather
inefficient. Another option is to use environments and pretend that
the key is a variable name:

e <- new.env()

This has the advantage that environments, contrary to lists, really
are hashed. Take a peek inside envir.c if you care.

(Abandon all hopes of S-PLUS compatibility if you do this, though.
Also beware that environments are slightly strange objects since they
are never duplicated - e.g. on assignment.)

   O__  ---- Peter Dalgaard             Blegdamsvej 3  
  c/ /'_ --- Dept. of Biostatistics     2200 Cph. N   
 (*) \(*) -- University of Copenhagen   Denmark      Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)             FAX: (+45) 35327907
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