Suppress automatic output to console in R

The issue is due to the fact that the function has multiple print statements, where stop, warning, or message would have been appropriate so that people can use suppressWarnings or suppressMessages.

You can work arount it using invisible(capture.output()) around your whole assignment (not just the right side).

f1 <- function(n, ...){
    print("Random print statement")
    cat("Random cat statement\n")
    rnorm(n = n, ...)
}

f1(2)
#> [1] "Random print statement"
#> Random cat statement
#> [1] -0.1115004 -1.0830523
invisible(capture.output(x <- f1(2)))
x
#> [1]  0.0464493 -0.1453540

See also suppress messages displayed by "print" instead of "message" or "warning" in R.