One learner execute mean, hoping to see the source code of mean function. However, he saw this:

function (x, ...) 
UseMethod("mean")
<bytecode: 0x7fa151cbe038>
<environment: namespace:base>

, which is not really code.

Question: How to know how mean was created?

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It needs some advanced knowledge of R language to fully understand the mechanism, which is covered in another course, Advanced R Programming. If you’re not aiming to be an R developer, that course may not necessary though.

Still you can try these codes:

methods(mean)
# You should see several elements looking like mean.XXX
getAnywhere(mean.default)
# This is the source code you want

Here is some brief explanation. In fact, mean is a “generic function” in R, which means that it can return different kinds of values depending on the class of inputs. The supported classes can be found in the results of methods(mean), so we know the mean function can actually calculate the mean of numeric values, or a series of dates or time points. Users don’t usually specify the method explicitly, but just keep in mind that things work in that way.

There are also discussions on StackOverflow, like Looking at internal Methods.