[R] Pasting with Quotes

[David Winsemius]

On May 5, 2012, at 2:42 PM, Josh Browning wrote:

> Hello useRs!
>
> So, I have a random question.  I'm trying to build a character  
> string, then
> evaluate it.

Actually you are trying to build a language object , a call or an  
expression. You might have gotten further with:

do.call(ksvm, list(  ... named arguments ...)

>  I think an example would be the easiest way to explain:
>
>
>    kern.vec = c("rbfdot","polydot")
>    for( j in 1:length( kern.vec ) )
>    {
>      formula    = paste("ksvm( ind ~ . ,
> data=d.temp[,c(ind_col,dep_cols)], kernel =",kern.vec[j],",  
> prob.model=T )")
>      svm    = eval( parse( text=formula ) )
>     ...
>    }
>
>
> The problem I always seem to have is that in the formula, I need to  
> have
> quotes around "rbfdot" (for example).  But, when I paste the  
> expression
> together, it removes the quotes.  Is there a better way to do this  
> (or at
> least a way around this problem)?  My method seems a bit kludgy :)

Perhaps looking at either:

?substitute
?bquote

kern.vec = c("rbfdot","polydot")
    for( j in 1:length( kern.vec ) )
    {
      formula    = bquote(expression( ksvm( ind ~ . ,  
data=d.temp[,c(ind_col,dep_cols)], kernel =.(kern.vec[j] ) ,  
prob.model=T ) ))
      print(formula)
    }

expression(ksvm(ind ~ ., data = d.temp[, c(ind_col, dep_cols)],
     kernel = "rbfdot", prob.model = T))
expression(ksvm(ind ~ ., data = d.temp[, c(ind_col, dep_cols)],
     kernel = "polydot", prob.model = T))

Notice that the values for kern.vec are 'character' which is what you  
passed them (and what you seem to be requesting. If you wanted the  
values of those named objects you might try get(<name>). (I'm not a  
user of whatever package has `ksvm` in it, so I'm not aware of whether  
'rbfdot' is supposed to be a character value as a parameter or if  
those are named objects, and I'm not running out to identify the  
package and then to locate a working example to test the eval-result.  
Those are details you should have provided.)
>


-- 

David Winsemius, MD
West Hartford, CT