isR: Are we using R, rather than S?
In robertzk/monadicbase: The R Base Package

Description Usage Details Value See Also Examples

Test if running under R.

is.R()

The function has been written such as to correctly run in all versions of R, S and S-PLUS. In order for code to be runnable in both R and S dialects previous to S-PLUS 8.0, your code must either define is.R or use it as

if (exists("is.R") && is.function(is.R) && is.R()) {
## R-specific code
} else {
## S-version of code
}

is.R returns TRUE if we are using R and FALSE otherwise.

R.version, system.

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x <- stats::runif(20); small <- x < 0.4
## In the early years of R, 'which()' only existed in R:
if(is.R()) which(small) else seq(along = small)[small]