[R] repeating the same variable in formula

[Subirana Cachinero, Isaac]

I am using terms.formula function to substract the variables from a formula environment.

Concretely, with the attr(*, "term.labels") I get the right side terms specified in the formula.

However, when introducing the same variable two or more times, this appears only once.

For example, when typing



>f <- y ~ cholesterol + age + age

>attr(terms(f),"term.labels")



I get



[1] "cholesterol" "age"



and I would like to get



[1] "cholesterol" "age" "age"





Is it possible with terms.formula function to obtain the variables and the times that they are specified in the formula? Or may I use another function?



Thanks in advance.



Isaac.


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