How to reliably get dependent variable name from formula object?

Question

Let\'s say I have the following formula:

myformula<-formula(\"depVar ~ Var1 + Var2\")

How to reliably get dependent variable name from formu

Answer 1

Using all.vars is very tricky as it won't detect the response from a one-sided formula. For example

all.vars(~x+1)
[1] "x"

that is wrong.

Here is the most reliable way of getting the response:

    getResponseFromFormula = function(formula) {
        if (attr(terms(as.formula(formula))    , which = 'response'))
            all.vars(formula)[1]
        else
            NULL
    }


getResponseFromFormula(~x+1)
NULL

 getResponseFromFormula(y~x+1)
[1] "y"

Note that you can replace all.vars(formula)[1] in the function with formula[2] if the formula contains more than one variable for the response.