[R] Hashes as S4 Classes, or: How to separate environments
For learning purposes mainly I attempted to implement hashes/maps/dictionaries
(Python lingua) as S4 classes, see the coding below. I came across some rough S4
edges, but in the end it worked (for one dictionary).
When testing ones sees that the dictionaries D1 and D2 share their environments
[EMAIL PROTECTED] and [EMAIL PROTECTED], though I thought a new and empty
environment would be
generated each time 'new(Dict)' is called.
QUESTION: How can I separate the environments [EMAIL PROTECTED] and [EMAIL
PROTECTED] ?
Reading the articles mentioned in Tipps and Tricks didn't help me really.
Of course, I will welcome other corrections and improvements as well.
Working in R 2.7.0 under Windows.
Hans Werner
#-- Class and method definition for dictionaries ---
setClass(Dict,
representation (hash = environment),
prototype (hash = new.env(hash=T, parent = emptyenv()))
)
setMethod(show, signature(object=Dict),
definition = function(object) ls([EMAIL PROTECTED])
)
setGeneric(hclear, function(object) standardGeneric(hclear))
setMethod(hclear, signature(object=Dict),
function(object) rm(list=ls([EMAIL PROTECTED]), [EMAIL PROTECTED])
)
setGeneric(hput, function(object, key, value) standardGeneric(hput))
setMethod(hput, signature(object=Dict, key=character, value=ANY),
function(object, key, value) assign(key, value, [EMAIL PROTECTED])
)
setGeneric(hget, function(object, key, ...) standardGeneric(hget))
setMethod(hget, signature(object=Dict, key=character),
function(object, key) {
if (exists(key, [EMAIL PROTECTED], inherits = FALSE)) {
get(key, [EMAIL PROTECTED])
} else {
return(NULL)
}
}
)
# Some tests
D1 - new(Dict)
hput(D1, a, 1) # Same as: [EMAIL PROTECTED] - 1
hput(D1, b, 2)
hget(D1, a)
hget(D1, b)
show(D1)
D2 - new(Dict)
hput(D2, c, 3)
hput(D2, d, 4)
hget(D2, a) # Wrong: was defined only for D1
hget(D2, b)
show(D2)
hclear(D2) # Wrong: clears D1 too
show(D1)
#-
__
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Re: [R] Hashes as S4 Classes, or: How to separate environments
Hi Hans --
Hans W Borchers [EMAIL PROTECTED] writes:
For learning purposes mainly I attempted to implement hashes/maps/dictionaries
(Python lingua) as S4 classes, see the coding below. I came across some rough
S4
edges, but in the end it worked (for one dictionary).
When testing ones sees that the dictionaries D1 and D2 share their
environments
[EMAIL PROTECTED] and [EMAIL PROTECTED], though I thought a new and empty
environment would be
generated each time 'new(Dict)' is called.
QUESTION: How can I separate the environments [EMAIL PROTECTED] and [EMAIL
PROTECTED] ?
The prototype is created once, at class creation time. So all objects
derived from the prototype share the same environment (other types
like 'list' would have the illusion of being created anew, because of
copy-on-change semantics). A solution is to have an initialize method
that recreates the hash each time.
setMethod(initialize, signature=signature(.Object=Dict),
function(.Object,
hash=new.env(hash=TRUE, parent=emptyenv()),
...) {
callNextMethod(.Object, hash=hash, ...)
})
Another solution is to have a constructor that feeds Dict a new
environment
Dict - function() {
new(Dict, hash=new.env(hash=TRUE, parent=emptyenv())
}
The latter is perhaps preferable, both from an aesthetic / user point
of view ('Dict()' better than 'new(Dict)') and from the
nuances-of-S4 point of view (e.g., the default 'initialize' method is
documented, though not in so many words, as a copy constructor, taking
slots in it's first argument as defaults; 'initialize' above does not
satisfy that contract).
I know others have implemented Dict objects; it would be fun to hear
from them.
Martin
Reading the articles mentioned in Tipps and Tricks didn't help me really.
Of course, I will welcome other corrections and improvements as well.
Working in R 2.7.0 under Windows.
Hans Werner
#-- Class and method definition for dictionaries
---
setClass(Dict,
representation (hash = environment),
prototype (hash = new.env(hash=T, parent = emptyenv()))
)
setMethod(show, signature(object=Dict),
definition = function(object) ls([EMAIL PROTECTED])
)
setGeneric(hclear, function(object) standardGeneric(hclear))
setMethod(hclear, signature(object=Dict),
function(object) rm(list=ls([EMAIL PROTECTED]), [EMAIL PROTECTED])
)
setGeneric(hput, function(object, key, value) standardGeneric(hput))
setMethod(hput, signature(object=Dict, key=character, value=ANY),
function(object, key, value) assign(key, value, [EMAIL PROTECTED])
)
setGeneric(hget, function(object, key, ...) standardGeneric(hget))
setMethod(hget, signature(object=Dict, key=character),
function(object, key) {
if (exists(key, [EMAIL PROTECTED], inherits = FALSE)) {
get(key, [EMAIL PROTECTED])
} else {
return(NULL)
}
}
)
# Some tests
D1 - new(Dict)
hput(D1, a, 1) # Same as: [EMAIL PROTECTED] - 1
hput(D1, b, 2)
hget(D1, a)
hget(D1, b)
show(D1)
D2 - new(Dict)
hput(D2, c, 3)
hput(D2, d, 4)
hget(D2, a) # Wrong: was defined only for D1
hget(D2, b)
show(D2)
hclear(D2) # Wrong: clears D1 too
show(D1)
#-
__
R-help@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
--
Martin Morgan
Computational Biology / Fred Hutchinson Cancer Research Center
1100 Fairview Ave. N.
PO Box 19024 Seattle, WA 98109
Location: Arnold Building M2 B169
Phone: (206) 667-2793
__
R-help@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
Re: [R] Hashes as S4 Classes, or: How to separate environments
On May 10, 2008, at 7:30 AM, Hans W Borchers wrote:
For learning purposes mainly I attempted to implement hashes/maps/
dictionaries
(Python lingua) as S4 classes, see the coding below. I came across
some rough S4
edges, but in the end it worked (for one dictionary).
When testing ones sees that the dictionaries D1 and D2 share their
environments
[EMAIL PROTECTED] and [EMAIL PROTECTED], though I thought a new and empty environment
would be
generated each time 'new(Dict)' is called.
QUESTION: How can I separate the environments [EMAIL PROTECTED] and [EMAIL
PROTECTED] ?
The problem you are encountering is that the prototype is only
created once. Because environments are passed by reference, [EMAIL PROTECTED]
and [EMAIL PROTECTED] are the exact same environment:
D1 - new(Dict)
D1
[EMAIL PROTECTED]
environment: 0x182ac870
D2 - new(Dict)
[EMAIL PROTECTED]
environment: 0x182ac870
You have assumed that setClass will be executed for each new
dictionary, or at least that the prototype(...) part of it would run
each time. Not wanting right now to dig into the internals of
setClass, my guess is that it only creates a prototype once, and then
just reuses it each time, with something like an assignment operator.
One solution, very similar to what Martin just suggested, is below. I
believe another solution might be to have the hash be a list
containing an environment, though I haven't tried that.
The solution is to create a constructor function, the function
newDict below:
setClass(Dict,
representation (hash = environment))
)
newDict - function() {
obj - new(Dict)
[EMAIL PROTECTED] - new.env(hash=T, parent = emptyenv())
obj
}
In practice, you would probably want newDict to accept an arguments,
which may be a list or another Dict object, and then use that as a
starting point for the new hash.
Here's a sample run:
# Some tests
D1 - newHash()
D2 - newHash()
[EMAIL PROTECTED]
environment: 0x1e80c98
[EMAIL PROTECTED]# Notice the different address
environment: 0x1e868fc
hput(D1, a, 1)
hget(D1, a)
[1] 1
show(D1)
[1] a
hput(D2, c, 3)
hget(D2, a) # Does the correct thing this time
NULL
hget(D2, c)
[1] 3
show(D2)
[1] c
hclear(D2)
show(D1)# Works properly now
[1] a
#-
Haris Skiadas
Department of Mathematics and Computer Science
Hanover College
Reading the articles mentioned in Tipps and Tricks didn't help me
really.
Of course, I will welcome other corrections and improvements as well.
Working in R 2.7.0 under Windows.
Hans Werner
#-- Class and method definition for dictionaries
---
setClass(Dict,
representation (hash = environment),
prototype (hash = new.env(hash=T, parent = emptyenv()))
)
setMethod(show, signature(object=Dict),
definition = function(object) ls([EMAIL PROTECTED])
)
setGeneric(hclear, function(object) standardGeneric(hclear))
setMethod(hclear, signature(object=Dict),
function(object) rm(list=ls([EMAIL PROTECTED]), [EMAIL PROTECTED])
)
setGeneric(hput, function(object, key, value) standardGeneric
(hput))
setMethod(hput, signature(object=Dict, key=character,
value=ANY),
function(object, key, value) assign(key, value, [EMAIL PROTECTED])
)
setGeneric(hget, function(object, key, ...) standardGeneric(hget))
setMethod(hget, signature(object=Dict, key=character),
function(object, key) {
if (exists(key, [EMAIL PROTECTED], inherits = FALSE)) {
get(key, [EMAIL PROTECTED])
} else {
return(NULL)
}
}
)
# Some tests
D1 - new(Dict)
hput(D1, a, 1) # Same as: [EMAIL PROTECTED] - 1
hput(D1, b, 2)
hget(D1, a)
hget(D1, b)
show(D1)
D2 - new(Dict)
hput(D2, c, 3)
hput(D2, d, 4)
hget(D2, a) # Wrong: was defined only for D1
hget(D2, b)
show(D2)
hclear(D2) # Wrong: clears D1 too
show(D1)
#-
__
R-help@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
