R function with variable args depending on presence/absence of other args -

i've stumbled upon varargs issue in r 2 or 3 times, seems problem have little bit trickier expected. here is

i have function, variables, introduce variable, kind of flag, selects way function working , parameters needed function itself: namely number , type of inputs depends on (flag) input.

ok, example better:

example = function(x,flag=1,y){     if (flag) return(x)     else return(y) } 

and working fine. point in example need specify both x , y every time. instead function taking only x if flag=1 , only y if flag=0. (in stupid example 2 distinct functions, in actual case have other (common) arguments on calculations both 'parts' of functions need).

i know 1 may specify whatever value unused argument , result wouldn't change, want function readable user, , cumbersome need specify argument won't used function

thank help

what following.

example = function(x,flag=1,y){   if (flag && !missing(x)) return(x)   else if(!flag && !missing(y)) return(y) } 

this check if flag 0 or non-zero plus check if argument missing. may want handle case when neither of these true cause function return null in case.