How do you determine the namespace of a function?

Question

Given a function, how do you determine which namespace it has come from?

For example, if I type mean.default at the command prompt, the output includes

Answer 1

This function searches functions in the loaded namespaces and global environment:

getEnvName <- function(f) {
    attached <- c(environmentName(.GlobalEnv), loadedNamespaces())
    envs <- c(.GlobalEnv, lapply(attached[-1], .getNamespace))
    attached[vapply(envs, function(env) exists(f, env, inherits = FALSE), logical(1))]
}
median <- function() {}
getEnvName("median")
#> [1] "R_GlobalEnv" "stats"
getEnvName(".try_quietly")
#> [1] "tools"
getEnvName("getEnvName")
#> [1] "R_GlobalEnv"