single, double or no quotes in expression

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single, double or no quotes in expression

capy_bara
Dear all,

I am confused about how to create an expression. I use a package (rsbml) which uses expressions and seems to make a difference if there is a quote around the expression or not.

For example, package works with expressions such as
> expression(A + B)
but not with
> expression("A + B")

I now have a set of math expressions represented as strings, something like this:
> rhs_eq<- c("0", "A + B", "B * (2+C)")
and want to make expressions without quotes out of it.

I tried
> lapply(lapply(rhs_eq, as.symbol), as.expression)
which only turns the double quotes into single quotes, but does not remove the quotes.
I also played around with as.formula, as.name, quote and enquote, but had no success.  

Does anyone know about quotes in the expression data type?

Thanks in advance,

Hannes
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Re: single, double or no quotes in expression

Sarah Goslee
Hi,

You don't provide a reproducible example, but I suspect what you need is
parse():

> parse(text = "A + B")
expression(A + B)

Sarah

On Thu, Mar 15, 2012 at 10:55 AM, capy_bara <[hidden email]> wrote:

> Dear all,
>
> I am confused about how to create an expression. I use a package (rsbml)
> which uses expressions and seems to make a difference if there is a quote
> around the expression or not.
>
> For example, package works with expressions such as
>> expression(A + B)
> but not with
>> expression("A + B")
>
> I now have a set of math expressions represented as strings, something like
> this:
>> rhs_eq<- c("0", "A + B", "B * (2+C)")
> and want to make expressions without quotes out of it.
>
> I tried
>> lapply(lapply(rhs_eq, as.symbol), as.expression)
> which only turns the double quotes into single quotes, but does not remove
> the quotes.
> I also played around with as.formula, as.name, quote and enquote, but had no
> success.
>
> Does anyone know about quotes in the expression data type?
>
> Thanks in advance,
>
> Hannes
>
>

--
Sarah Goslee
http://www.functionaldiversity.org

______________________________________________
[hidden email] 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.
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Re: single, double or no quotes in expression

David Winsemius
In reply to this post by capy_bara

On Mar 15, 2012, at 10:55 AM, capy_bara wrote:

> Dear all,
>
> I am confused about how to create an expression. I use a package  
> (rsbml)
> which uses expressions and seems to make a difference if there is a  
> quote
> around the expression or not.
>
> For example, package works with expressions such as
>> expression(A + B)
> but not with
>> expression("A + B")
>
> I now have a set of math expressions represented as strings,  
> something like
> this:
>> rhs_eq<- c("0", "A + B", "B * (2+C)")
> and want to make expressions without quotes out of it.
>
> I tried
>> lapply(lapply(rhs_eq, as.symbol), as.expression)
> which only turns the double quotes into single quotes, but does not  
> remove
> the quotes.
> I also played around with as.formula, as.name, quote and enquote,  
> but had no
> success.
>
> Does anyone know about quotes in the expression data type?

 > parse(text=rhs_eq)
expression(0, A + B, B * (2+C))
 > parse(text=rhs_eq)[1]
expression(0)
 > parse(text=rhs_eq)[2]
expression(A + B)
 > parse(text=rhs_eq)[3]
expression(B * (2+C))


>
> Thanks in advance,
>
> Hannes
>
>
> --
> View this message in context: http://r.789695.n4.nabble.com/single-double-or-no-quotes-in-expression-tp4475247p4475247.html
> Sent from the R help mailing list archive at Nabble.com.
>
> ______________________________________________
> [hidden email] 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.

David Winsemius, MD
West Hartford, CT

______________________________________________
[hidden email] 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.
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Re: single, double or no quotes in expression

capy_bara
Many thanks,
"parse" is exactly what I was looking for!!

Hannes