[R] if/else help

[Crombie, Burnette N]

If a data.frame (r4) does not exist in my R environment, I would like to create it before I move on to the next step in my script. How do I make that happen?  Here is what I want to do from a code perspective:

if (exists(r4))
{
is.data.frame(get(r4))
}
else
{
a <- 0, b <- 0, c <- 0, d <- "x", r4 <- data.frame(cbind(a,b,c,d))
}

Thanks for your help,
B

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