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revallmevaluationexpression-evaluation

Evaluate strings for regression

From these strings

data = "mtcars"
y    = "mpg"
x    = c("cyl","disp")

, I am trying to perform a linear model. I tried things like

epp=function(x) eval(parse(text=paste0(x,collapse="+")))

lm(data=epp(data),epp(y)~epp(x))
# Error in eval(expr, envir, enclos) : object 'cyl' not found

where the last line was aimed to be equivalent to 

lm(data=mtcars,mpg~cyl+disp)
Solution

  • This involves two operations that are both described in multiple SO entries that use perhaps singly either the get or as.formula functions:

    lm(data=get(data), 
   formula=as.formula( paste( y, "~", paste(x, collapse="+") ) )
  )

    In both cases you are use a text/character object to return a language object. In the first argument get returns a 'symbol' that can be evaluated and in the second instance as.formula returns a 'formula' object. @blmoore is correct in advising us that lm will accept a character object, so the as.formula call is not needed here.