R help - Mar 2011 - string evaluation

Good morning, dear listers

I am wondering how to do string evaluation such that

model <- glm(Y ~ [STRING], data = mydata) where STRING <- "x1 + x2 +
x3"

It is very doable in other language such as SAS.

Thank you so much for your insight!

On Mar 12, 2011, at 10:10 AM, Wensui Liu wrote:
> Good morning, dear listers
>
> I am wondering how to do string evaluation such that
>
> model <- glm(Y ~ [STRING], data = mydata) where STRING <- "x1 +
x2 +
> x3"
>
> It is very doable in other language such as SAS.
Also "very doable" in R. You need to understand that R is a bit more  
structured than SAS, which is really just a macro-processor at least  
by heritage. Formulas are a language class in R and not just character  
vectors,  so you need to construct them outside the regression  
functions.

STRING <- "x1 + x2 + x3"
form <- formula(paste("Y ~ ", STRING) )
  form
# Y ~ x1 + x2 + x3
  class(form)
#[1] "formula"

  model <- glm(form, data = mydata)

-- 
David Winsemius, MD
West Hartford, CT

Thank you so much, David. Your solution exactly suits my need.

formula() seems the key.

appreciate your help!

On Sat, Mar 12, 2011 at 10:22 AM, David Winsemius
<dwinsemius at comcast.net> wrote:
>
> On Mar 12, 2011, at 10:10 AM, Wensui Liu wrote:
>
>> Good morning, dear listers
>>
>> I am wondering how to do string evaluation such that
>>
>> model <- glm(Y ~ [STRING], data = mydata) where STRING <-
"x1 + x2 + x3"
>>
>> It is very doable in other language such as SAS.
>
> Also "very doable" in R. You need to understand that R is a bit
more
> structured than SAS, which is really just a macro-processor at least by
> heritage. Formulas are a language class in R and not just character
vectors,
> ?so you need to construct them outside the regression functions.
>
> STRING <- "x1 + x2 + x3"
> form <- formula(paste("Y ~ ", STRING) )
> ?form
> # Y ~ x1 + x2 + x3
> ?class(form)
> #[1] "formula"
>
> ?model <- glm(form, data = mydata)
>
> --
> David Winsemius, MD
> West Hartford, CT
>
>


-- 
=============================WenSui Liu
Credit Risk Manager, 53 Bancorp
wensui.liu at 53.com
513-295-4370
==============================