hashing using named lists

You could try using environments:

 > e <- new.env(hash = TRUE)
 > e$new <- 1:4
 > ls(e)
[1] "new"
 > e$new
[1] 1 2 3 4
 > e$ne
NULL

-roger

hi all,
I am trying to use named list to hash a bunch of vector by name, for 
instance:
test = list()
test$name = c(1,2,3)

the problem is that when i try to get the values back by using the name, 
the matching isn't done in an exact way, so
test$na is not NULL.

is there a way around this?
Why by default all.equal.list doesnt require an exact match?
How can I do hashing in R?

thanks.
ulas.

______________________________________________
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Roger D. Peng
http://www.biostat.jhsph.edu/~rpeng/

hi all,
I am trying to use named list to hash a bunch of vector by name, for 
instance:
test = list()
test$name = c(1,2,3)

the problem is that when i try to get the values back by using the name, the 
matching isn't done in an exact way, so
test$na is not NULL.

is there a way around this?

?match on the names

Why by default all.equal.list doesnt require an exact match?

What do you mean by that?  It (by default or not) tests all the 
attributes, including the names:

test <- list(name=1:3)
test2 <- list(na=1:3)
all.equal(test, test2)
[1] "Names: 1 string mismatches"

Now, all.equal does not require an exact match, deliberately: that is what 
identical() is for:

identical(test, test2)
[1] FALSE

How can I do hashing in R?

?match

Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

is there a way around this?

yes...

Why by default all.equal.list doesnt require an exact match?

because we're lazy? :)

How can I do hashing in R?

you can explicitly test the names for equality, eg with this 2-element 
list:

  > x
  $name
  [1] 1 2 3

  $n
  [1] 3 2 1

  You can do:

  > x[names(x)=='name']
  $name
  [1] 1 2 3

  > x[names(x)=='na']
  list()

  > x[names(x)=='n']
  $n
  [1] 3 2 1

  Of course, the right way would be to create a new class, 'hash' 
perhaps, that did all this in its '$' or '[' methods.

Baz

Use match() for exact matching,

i.e.,

 > test[[match("name", names(test))]]

Yes, it is more cumbersome.  This partial matching is considered by some to 
be a design fault, but changing it would break too many programs that 
depend upon it.

I don't understand your question about all.equal.list() -- it does seem to 
require exact matches on names, e.g.:

 > all.equal(list(a=1:3), list(aa=1:3))
[1] "Names: 1 string mismatches"
 > all.equal(list(aa=1:3), list(a=1:3))
[1] "Names: 1 string mismatches"
 >

(the above run in R 2.0.0)

-- Tony Plate

(BTW, in R this operation is generally called "indexing" or "subscripting" 
or "extraction", but not "hashing".  "Hashing" is a specific technique for 
managing and looking up indices, which is why some other programming 
languages refer to list-like objects that are indexed by character strings 
as "hashes".  I don't think hashing is used for list names in R, but 
someone please correct me if I'm wrong! )

hi all,
I am trying to use named list to hash a bunch of vector by name, for instance:
test = list()
test$name = c(1,2,3)

the problem is that when i try to get the values back by using the name, 
the matching isn't done in an exact way, so
test$na is not NULL.

is there a way around this?
Why by default all.equal.list doesnt require an exact match?
How can I do hashing in R?

thanks.
ulas.

______________________________________________
R-help at stat.math.ethz.ch mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html