R help - Mar 2011 - altering a "call" variable from quote()

I have a variable of mode "call":
> b = quote(b==3)
> b
b == 3

Now I want to append "&& x > 2" to the value of b. How do I
do that?

Jack Tanner <ihok <at> hotmail.com> writes:
> > b = quote(b==3)
> 
> Now I want to append "&& x > 2" to the value of b. How
do I do that?
Never mind, I figured it out:

substitute(b && x > 2, list(b=b))

> -----Original Message-----
> From: r-help-bounces at r-project.org 
> [mailto:r-help-bounces at r-project.org] On Behalf Of Jack Tanner
> Sent: Sunday, March 27, 2011 9:14 PM
> To: r-help at stat.math.ethz.ch
> Subject: Re: [R] altering a "call" variable from quote()
> 
> Jack Tanner <ihok <at> hotmail.com> writes:
> 
> > > b = quote(b==3)
> > 
> > Now I want to append "&& x > 2" to the value of
b. How do I do that?
> 
> Never mind, I figured it out:
> 
> substitute(b && x > 2, list(b=b))
You can also use call() or as.call(): 
  > e1 <- substitute(b && x > 2, list(b=b))
  > e2 <- call("&&", b, quote(x>2))
  > e3 <- as.call(list(quote(`&&`), b, quote(x>2)))
  > identical(e1,e2) && identical(e1,e3)
  [1] TRUE
substitute can be a pain when the first argument is not
a literal expression.

Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com  
> 
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On Mar 28, 2011, at 11:32 AM, William Dunlap wrote:
>> -----Original Message-----
>> From: r-help-bounces at r-project.org
>> [mailto:r-help-bounces at r-project.org] On Behalf Of Jack Tanner
>> Sent: Sunday, March 27, 2011 9:14 PM
>> To: r-help at stat.math.ethz.ch
>> Subject: Re: [R] altering a "call" variable from quote()
>>
>> Jack Tanner <ihok <at> hotmail.com> writes:
>>
>>>> b = quote(b==3)
>>>
>>> Now I want to append "&& x > 2" to the value
of b. How do I do that?
>>
>> Never mind, I figured it out:
>>
>> substitute(b && x > 2, list(b=b))
>
> You can also use call() or as.call():
>> e1 <- substitute(b && x > 2, list(b=b))
>> e2 <- call("&&", b, quote(x>2))
>> e3 <- as.call(list(quote(`&&`), b, quote(x>2)))
>> identical(e1,e2) && identical(e1,e3)
>  [1] TRUE
> substitute can be a pain when the first argument is not
> a literal expression.
Or `bquote`:

  b = quote(b==3)
  bquote(.(b) && x > 2)
# b == 3 && x > 2

 > identical(e1,e2) &&
+ identical(e1,e3) &&
+ identical(e1, bquote(.(b) && x > 2) )
[1] TRUE

>
> Bill Dunlap
> Spotfire, TIBCO Software
> wdunlap tibco.com
David Winsemius, MD
West Hartford, CT