R trouble with substitute when formula writing -

I want to iterate on a form where the independent variable has been passed as a string. I am using the option and expression but I do not know why it is unsuccessful.

Please see the following:

  & gt; Coxph (substitute (survivaloutcome ~ x, list (x = as.name) (colnames (combineddata) [1]))), data = combined data Error in default (formula, special, data = data): no rule element nor specialty & gt; Option (the result of existence ~ x, list (x = as is. Name (colnames (combined data) [1])). The result of survival ~ PMM 2 & gt; Coxf (SurvivalFfects- PMM2, Data = Combined Data) Calls: Coxf (Formula = ExertaFacture ~ PMM2, Data = Combined Data) from COF Exp (COF) GP PMM 2 0.0445 1.05 0.146 0.305 0.76 1 DF-based educational ratios test = 0.0 9, p = 0.761n = 206, number of events = 12 9> & Gt; Colnames [1] [1] "PMM2"  

As you can see, the expression completely matches, but I do not know why this fails is?