[R] Communicating from one function to another
My question is a seemingly simple one. I have a bunch of user-defined
functions which compute such-and-such objects. I want to be able to define a
variable in a particular function, then make use of it later, perhaps in a
different function, without necessarily having to move it around in argument
lists. In the C community, it would be called a global variable.
Question 1: Is this practical at all in the R language?
Suppose the variable is called x23. I want to assign a value to it, then use
it later. Seemingly, there are two cases:
Case I is if the variable is given its value at the top level.
Case II is if it is given its value inside a user-defined function. That I
do not know how to do.
Example:
func1 - function (){
x23 - 2.6
return ()
}
driver_func - function (){
func1 ()
print (x23)
return ()
}
However, when I call driver_func, it won't work. Beginning with the load
operation, I get:
Type 'demo()' for some demos, 'help()' for on-line help, or
'help.start()' for an HTML browser interface to help.
Type 'q()' to quit R.
func1 - function (){
+
+ x23 - 2.6
+
+ return ()
+
+ }
driver_func - function (){
+
+ func1 ()
+
+ print (x23)
+
+ return ()
+
+ }
driver_func ()
Error in print(x23) : object x23 not found
---
From Tom:
Clearly, the two functions cannot communicate. I am aware of the existence
of environments, but don't know much about them. Also, the attach function
and the get and set functions. Also, .GlobalEnv It might or might not make
sense to create a list of all of the variables, with two functions which
get all of them and set all of them. The function calls may be thought of as
an upside down tree. I want to be able to communicate from any node to any
other node.
Your advice?
Tom
Thomas L. Jones, PhD, Computer Science
__
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
Re: [R] Communicating from one function to another
Thomas L Jones wrote:
My question is a seemingly simple one. I have a bunch of user-
defined functions which compute such-and-such objects. I want to be
able to define a variable in a particular function, then make use of
it later, perhaps in a different function, without necessarily
having to move it around in argument lists. In the C community, it
would be called a global variable.
Global variables in R are used with - instead of -.
For example:
x - 1
y - 1
f - function() {
x - 2
y - 2
}
f()
will turn y to 2 but will not change x.
Alberto Monteiro
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and provide commented, minimal, self-contained, reproducible code.
Re: [R] Communicating from one function to another
On 11/26/2007 1:25 PM, Alberto Monteiro wrote:
Thomas L Jones wrote:
My question is a seemingly simple one. I have a bunch of user-
defined functions which compute such-and-such objects. I want to be
able to define a variable in a particular function, then make use of
it later, perhaps in a different function, without necessarily
having to move it around in argument lists. In the C community, it
would be called a global variable.
Global variables in R are used with - instead of -.
For example:
x - 1
y - 1
f - function() {
x - 2
y - 2
}
f()
will turn y to 2 but will not change x.
R doesn't really have global variables. - goes looking in parent
environments until it finds the target variable, and makes the
assignment there. If it never finds one, it makes the assignment in the
global environment, but the name is misleading: it should really be
called the user workspace.
Duncan Murdoch
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
Re: [R] Communicating from one function to another
Duncan Murdoch wrote:
R doesn't really have global variables. - goes looking in parent
environments until it finds the target variable, and makes the
assignment there. If it never finds one, it makes the assignment in
the global environment, but the name is misleading: it should
really be called the user workspace.
Got it.
So, in this case:
x - 1
f - function() {
x - 2
g - function() {
x - 3
}
g()
x
}
f()
It's expected that f will return 3, but x would still be 1?
Alberto Monteiro
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and provide commented, minimal, self-contained, reproducible code.
Re: [R] Communicating from one function to another
On 11/26/2007 1:46 PM, Alberto Monteiro wrote:
Duncan Murdoch wrote:
R doesn't really have global variables. - goes looking in parent
environments until it finds the target variable, and makes the
assignment there. If it never finds one, it makes the assignment in
the global environment, but the name is misleading: it should
really be called the user workspace.
Got it.
So, in this case:
x - 1
f - function() {
x - 2
g - function() {
x - 3
}
g()
x
}
f()
It's expected that f will return 3, but x would still be 1?
Yes, the one in the user workspace be unaffected.
Duncan Murdoch
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and provide commented, minimal, self-contained, reproducible code.
Re: [R] Communicating from one function to another
Global variables are strongly discouraged in R, but there are sometimes
when they may be needed and so are possible.
One example where they are used is in random number generation, every
time a random number function is called (rnorm for example) the global
variable .Random.seed is updated so that new random values will be
generated next time.
If you absolutely need a global variable, then use assign (or possibly
-) to do the assignment. Also choose a name such that your global
variable is unlikely to overwright or be overwritten (if you use x, then
both are likely to happen, preferable to use a name starting with '.').
A better approach is to use variables in a local environment such that
the 2 functions can both see the variable, but nothing outside of that
environment can. Here is a simple example:
tmp - local({
+ x23 - numeric(1)
+ func1 - function(){
+ x23 - 2.6
+ }
+ func2 - function(){
+ print(x23)
+ }
+ list(func1=func1,func2=func2)
+ })
func1 - tmp$func1
func2 - tmp$func2
func2()
[1] 0
func1()
func2()
[1] 2.6
tmp$func2()
[1] 2.6
The local function creates a new environment in which everything in the
{} is evaluated/created. This new environment then gets a variable
(x23) which starts off to be 0. The 2 functions defined in the same
environment can access x23. The list statement just combines the 2
functions into a single object to be returned.
So after running local, the variable tmp is a list with 2 elements each
being a function, we can run them as
tmp$func2() or copy them to easier to use functions. We run func2 and
see that x23 is currently 0, then run func1 to change the value (don't
see anything yet) then run func2 again to see the new value of x23.
This is a cleaner solution in that if we already have a variable called
x23, it does not get overwritten by the global and it is very
difficult to accidentally overwrite the x23 shared by the 2 functions.
Hope this helps,
--
Gregory (Greg) L. Snow Ph.D.
Statistical Data Center
Intermountain Healthcare
[EMAIL PROTECTED]
(801) 408-8111
-Original Message-
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of Thomas L Jones, PhD
Sent: Monday, November 26, 2007 10:11 AM
To: R-project help
Subject: [R] Communicating from one function to another
My question is a seemingly simple one. I have a bunch of
user-defined functions which compute such-and-such objects. I
want to be able to define a variable in a particular
function, then make use of it later, perhaps in a different
function, without necessarily having to move it around in
argument lists. In the C community, it would be called a
global variable.
Question 1: Is this practical at all in the R language?
Suppose the variable is called x23. I want to assign a value
to it, then use it later. Seemingly, there are two cases:
Case I is if the variable is given its value at the top level.
Case II is if it is given its value inside a user-defined
function. That I do not know how to do.
Example:
func1 - function (){
x23 - 2.6
return ()
}
driver_func - function (){
func1 ()
print (x23)
return ()
}
However, when I call driver_func, it won't work. Beginning
with the load operation, I get:
Type 'demo()' for some demos, 'help()' for on-line help, or
'help.start()' for an HTML browser interface to help.
Type 'q()' to quit R.
func1 - function (){
+
+ x23 - 2.6
+
+ return ()
+
+ }
driver_func - function (){
+
+ func1 ()
+
+ print (x23)
+
+ return ()
+
+ }
driver_func ()
Error in print(x23) : object x23 not found
--
-
From Tom:
Clearly, the two functions cannot communicate. I am aware of
the existence of environments, but don't know much about
them. Also, the attach function and the get and set
functions. Also, .GlobalEnv It might or might not make sense
to create a list of all of the variables, with two
functions which get all of them and set all of them. The
function calls may be thought of as an upside down tree. I
want to be able to communicate from any node to any other node.
Your advice?
Tom
Thomas L. Jones, PhD, Computer Science
__
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.
__
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] Communicating from one function to another
Others have already answered your direct question but consider that
what you may want without realizing it is object-oriented programming.
Here p is a proto object with components x and f. x is a variable and f is a
method. The method f sets x to a. (Presumably in reality f would do other
things too but for this example that's all it does.) Before invoking
f, x is 0
and after invoking f x is 3. Lastly we invoke method g on proto object p and
get back 30.
library(proto)
p - proto(x = 0, f = function(., a) .$x - a, g = function(.) .$x * 10)
p$x # 0
p$f(3)
p$x # 3
p$g() # 30
See:
http:/r-proto.googlecode.com
for more.
On Nov 26, 2007 12:11 PM, Thomas L Jones, PhD [EMAIL PROTECTED] wrote:
My question is a seemingly simple one. I have a bunch of user-defined
functions which compute such-and-such objects. I want to be able to define a
variable in a particular function, then make use of it later, perhaps in a
different function, without necessarily having to move it around in argument
lists. In the C community, it would be called a global variable.
Question 1: Is this practical at all in the R language?
Suppose the variable is called x23. I want to assign a value to it, then use
it later. Seemingly, there are two cases:
Case I is if the variable is given its value at the top level.
Case II is if it is given its value inside a user-defined function. That I
do not know how to do.
Example:
func1 - function (){
x23 - 2.6
return ()
}
driver_func - function (){
func1 ()
print (x23)
return ()
}
However, when I call driver_func, it won't work. Beginning with the load
operation, I get:
Type 'demo()' for some demos, 'help()' for on-line help, or
'help.start()' for an HTML browser interface to help.
Type 'q()' to quit R.
func1 - function (){
+
+ x23 - 2.6
+
+ return ()
+
+ }
driver_func - function (){
+
+ func1 ()
+
+ print (x23)
+
+ return ()
+
+ }
driver_func ()
Error in print(x23) : object x23 not found
---
From Tom:
Clearly, the two functions cannot communicate. I am aware of the existence
of environments, but don't know much about them. Also, the attach function
and the get and set functions. Also, .GlobalEnv It might or might not make
sense to create a list of all of the variables, with two functions which
get all of them and set all of them. The function calls may be thought of as
an upside down tree. I want to be able to communicate from any node to any
other node.
Your advice?
Tom
Thomas L. Jones, PhD, Computer Science
__
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] Communicating from one function to another
On 11/26/07, Gabor Grothendieck [EMAIL PROTECTED] wrote: Others have already answered your direct question but consider that what you may want without realizing it is object-oriented programming. I agree with Gabor, you're not actually looking for a global state, but a mutable object (explicitly passing non-mutable objects around in argument lists and returns is called threading state). I've used the proto package quite a bit for mutable state, and it adds an often needed programming paradigm to R. Hadley -- http://had.co.nz/ __ 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.
