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Michael Friendly

2010-Mar-16 12:26 UTC

[R] function arguments: name of an object vs. call producing the object?

In a function, say foo.glm for glm objects I want to use the name of the 
object as a label for some output,
but *only* if a glm object was passed as an argument, not a call to 
glm() producing that object.
How can I distinguish these two cases?

For example, I can use the following to get the name of the argument:

foo.glm <- function(object) {
    oname <- as.character(sys.call())[2]
    oname
}

 > indep <- glm(Freq ~ mental + ses, family = poisson, data = Mental)
 > foo.glm(indep)
[1] "indep"

But in foo.glm() I want to avoid using this as oname:
 > foo.glm(glm(formula = Freq ~ mental + ses, family = poisson, data = 
Mental))
[1] "glm(formula = Freq ~ mental + ses, family = poisson, data =
Mental)"

Here is Mental, if it matters.

 dput(Mental)
structure(list(ses = structure(c(1L, 1L, 1L, 1L, 2L, 2L, 2L,
2L, 3L, 3L, 3L, 3L, 4L, 4L, 4L, 4L, 5L, 5L, 5L, 5L, 6L, 6L, 6L,
6L), .Label = c("1", "2", "3", "4",
"5", "6"), class = c("ordered",
"factor")), mental = structure(c(1L, 2L, 3L, 4L, 1L, 2L, 3L,
4L, 1L, 2L, 3L, 4L, 1L, 2L, 3L, 4L, 1L, 2L, 3L, 4L, 1L, 2L, 3L,
4L), .Label = c("Well", "Mild", "Moderate",
"Impaired"), class =
c("ordered",
"factor")), Freq = c(64L, 94L, 58L, 46L, 57L, 94L, 54L, 40L,
57L, 105L, 65L, 60L, 72L, 141L, 77L, 94L, 36L, 97L, 54L, 78L,
21L, 71L, 54L, 71L)), .Names = c("ses", "mental",
"Freq"), row.names =
c(NA,
-24L), class = "data.frame")

-- 
Michael Friendly     Email: friendly AT yorku DOT ca 
Professor, Psychology Dept.
York University      Voice: 416 736-5115 x66249 Fax: 416 736-5814
4700 Keele Street    http://www.math.yorku.ca/SCS/friendly.html
Toronto, ONT  M3J 1P3 CANADA

Duncan Murdoch

2010-Mar-16 12:44 UTC

head link

[R] function arguments: name of an object vs. call producing the object?

On 16/03/2010 8:26 AM, Michael Friendly wrote:> In a function, say foo.glm for glm objects I want to use the name of the 
> object as a label for some output,
> but *only* if a glm object was passed as an argument, not a call to 
> glm() producing that object.
> How can I distinguish these two cases?
Look at typeof(substitute(object)).  For example,

 > f <- function(object) typeof(substitute(object))
 > f(aname)
[1] "symbol"
 > f(aname+1)
[1] "language"

That will tell you if an object was passed by name, or if you got an 
expression to produce the object.

One problem with this approach is that it only looks at the direct call 
to f, for example

 > g <- function(x) f(x)
 > g(aname + 1)
[1] "symbol"

because substitute looks at the f(x) call, not the g(aname + 1) call.

Duncan Murdoch

> 
> For example, I can use the following to get the name of the argument:
> 
> foo.glm <- function(object) {
>     oname <- as.character(sys.call())[2]
>     oname
> }
> 
>  > indep <- glm(Freq ~ mental + ses, family = poisson, data = Mental)
>  > foo.glm(indep)
> [1] "indep"
> 
> But in foo.glm() I want to avoid using this as oname:
>  > foo.glm(glm(formula = Freq ~ mental + ses, family = poisson, data = 
> Mental))
> [1] "glm(formula = Freq ~ mental + ses, family = poisson, data =
Mental)"
> 
> Here is Mental, if it matters.
> 
>  dput(Mental)
> structure(list(ses = structure(c(1L, 1L, 1L, 1L, 2L, 2L, 2L,
> 2L, 3L, 3L, 3L, 3L, 4L, 4L, 4L, 4L, 5L, 5L, 5L, 5L, 6L, 6L, 6L,
> 6L), .Label = c("1", "2", "3", "4",
"5", "6"), class = c("ordered",
> "factor")), mental = structure(c(1L, 2L, 3L, 4L, 1L, 2L, 3L,
> 4L, 1L, 2L, 3L, 4L, 1L, 2L, 3L, 4L, 1L, 2L, 3L, 4L, 1L, 2L, 3L,
> 4L), .Label = c("Well", "Mild", "Moderate",
"Impaired"), class =
> c("ordered",
> "factor")), Freq = c(64L, 94L, 58L, 46L, 57L, 94L, 54L, 40L,
> 57L, 105L, 65L, 60L, 72L, 141L, 77L, 94L, 36L, 97L, 54L, 78L,
> 21L, 71L, 54L, 71L)), .Names = c("ses", "mental",
"Freq"), row.names =
> c(NA,
> -24L), class = "data.frame")
>

Michael Friendly

2010-Mar-16 16:16 UTC

head link

[R] function arguments: name of an object vs. call producing the object?

Thanks, Duncan

In my context, the following gives me what I want:

 > foo.glm <- function(object) {
+     if (typeof(substitute(object))=="symbol")
+     oname <- as.character(sys.call())[2]
+     else oname <- NULL
+     oname
+ }
 >
 >
 >
 > indep <- glm(Freq ~ mental + ses, family = poisson, data = Mental)
 > foo.glm(indep)
[1] "indep"
 >
 > foo.glm(glm(formula = Freq ~ mental + ses, family = poisson, data = 
Mental))
NULL
 >


Duncan Murdoch wrote:> On 16/03/2010 8:26 AM, Michael Friendly wrote:
>> In a function, say foo.glm for glm objects I want to use the name of 
>> the object as a label for some output,
>> but *only* if a glm object was passed as an argument, not a call to 
>> glm() producing that object.
>> How can I distinguish these two cases?
>
> Look at typeof(substitute(object)).  For example,
>
> > f <- function(object) typeof(substitute(object))
> > f(aname)
> [1] "symbol"
> > f(aname+1)
> [1] "language"
>
> That will tell you if an object was passed by name, or if you got an 
> expression to produce the object.
>
> One problem with this approach is that it only looks at the direct 
> call to f, for example
>
> > g <- function(x) f(x)
> > g(aname + 1)
> [1] "symbol"
>
> because substitute looks at the f(x) call, not the g(aname + 1) call.
>
> Duncan Murdoch
>
>
>>
>> For example, I can use the following to get the name of the argument:
>>
>> foo.glm <- function(object) {
>>     oname <- as.character(sys.call())[2]
>>     oname
>> }
>>
>>  > indep <- glm(Freq ~ mental + ses, family = poisson, data =
Mental)
>>  > foo.glm(indep)
>> [1] "indep"
>>
>> But in foo.glm() I want to avoid using this as oname:
>>  > foo.glm(glm(formula = Freq ~ mental + ses, family = poisson, data
>> = Mental))
>> [1] "glm(formula = Freq ~ mental + ses, family = poisson, data = 
>> Mental)"
>>
>> Here is Mental, if it matters.
>>
>>  dput(Mental)
>> structure(list(ses = structure(c(1L, 1L, 1L, 1L, 2L, 2L, 2L,
>> 2L, 3L, 3L, 3L, 3L, 4L, 4L, 4L, 4L, 5L, 5L, 5L, 5L, 6L, 6L, 6L,
>> 6L), .Label = c("1", "2", "3",
"4", "5", "6"), class = c("ordered",
>> "factor")), mental = structure(c(1L, 2L, 3L, 4L, 1L, 2L, 3L,
>> 4L, 1L, 2L, 3L, 4L, 1L, 2L, 3L, 4L, 1L, 2L, 3L, 4L, 1L, 2L, 3L,
>> 4L), .Label = c("Well", "Mild",
"Moderate", "Impaired"), class =
>> c("ordered",
>> "factor")), Freq = c(64L, 94L, 58L, 46L, 57L, 94L, 54L, 40L,
>> 57L, 105L, 65L, 60L, 72L, 141L, 77L, 94L, 36L, 97L, 54L, 78L,
>> 21L, 71L, 54L, 71L)), .Names = c("ses", "mental",
"Freq"), row.names
>> = c(NA,
>> -24L), class = "data.frame")
>>
>

-- 
Michael Friendly     Email: friendly AT yorku DOT ca 
Professor, Psychology Dept.
York University      Voice: 416 736-5115 x66249 Fax: 416 736-5814
4700 Keele Street    http://www.math.yorku.ca/SCS/friendly.html
Toronto, ONT  M3J 1P3 CANADA

Bert Gunter

2010-Mar-16 16:18 UTC

head link

[R] function arguments: name of an object vs. call producing theobject?

Michael:

Well, several possibilities come to mind, but their appropriateness depends
on what your argument could be.

1) The deparse(substitute(...)) construction will get you the character
string that was used as the argument and you can grep for "~" in it.

2) Or maybe check the class of the argument (e.g. if it's a formula it will
inherit from "formula").

3) Or create separate (S3) methods foo.glm, foo.formula, etc. for the
different classes that you wish to consider. This might be the cleanest
approach, but it requires more planning.

HTH

Bert Gunter
Genentech Nonclinical Biostatistics
 
 
-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org]
On
Behalf Of Michael Friendly
Sent: Tuesday, March 16, 2010 5:27 AM
To: R-Help
Subject: [R] function arguments: name of an object vs. call producing
theobject?

In a function, say foo.glm for glm objects I want to use the name of the 
object as a label for some output,
but *only* if a glm object was passed as an argument, not a call to 
glm() producing that object.
How can I distinguish these two cases?

For example, I can use the following to get the name of the argument:

foo.glm <- function(object) {
    oname <- as.character(sys.call())[2]
    oname
}

 > indep <- glm(Freq ~ mental + ses, family = poisson, data = Mental)
 > foo.glm(indep)
[1] "indep"

But in foo.glm() I want to avoid using this as oname:
 > foo.glm(glm(formula = Freq ~ mental + ses, family = poisson, data = 
Mental))
[1] "glm(formula = Freq ~ mental + ses, family = poisson, data =
Mental)"

Here is Mental, if it matters.

 dput(Mental)
structure(list(ses = structure(c(1L, 1L, 1L, 1L, 2L, 2L, 2L,
2L, 3L, 3L, 3L, 3L, 4L, 4L, 4L, 4L, 5L, 5L, 5L, 5L, 6L, 6L, 6L,
6L), .Label = c("1", "2", "3", "4",
"5", "6"), class = c("ordered",
"factor")), mental = structure(c(1L, 2L, 3L, 4L, 1L, 2L, 3L,
4L, 1L, 2L, 3L, 4L, 1L, 2L, 3L, 4L, 1L, 2L, 3L, 4L, 1L, 2L, 3L,
4L), .Label = c("Well", "Mild", "Moderate",
"Impaired"), class =
c("ordered",
"factor")), Freq = c(64L, 94L, 58L, 46L, 57L, 94L, 54L, 40L,
57L, 105L, 65L, 60L, 72L, 141L, 77L, 94L, 36L, 97L, 54L, 78L,
21L, 71L, 54L, 71L)), .Names = c("ses", "mental",
"Freq"), row.names =
c(NA,
-24L), class = "data.frame")

-- 
Michael Friendly     Email: friendly AT yorku DOT ca 
Professor, Psychology Dept.
York University      Voice: 416 736-5115 x66249 Fax: 416 736-5814
4700 Keele Street    http://www.math.yorku.ca/SCS/friendly.html
Toronto, ONT  M3J 1P3 CANADA

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