Hey there! Let's unpack everything you're asking about R's rep() function—super common to hit these little quirks when starting out, so great question.

1. How rep() actually works #

At its core, rep() is R's go-to function for repeating elements. The formal signature is:

rep(x, times = 1, length.out = NA, each = 1)

Let's break down the key parameters in plain terms:

• x: The element(s) you want to repeat (can be a single number, a vector, even a list)
• times: How many times to repeat the entire x collection. If x is a vector and times matches its length, it repeats each element of x the corresponding number of times from times.
• each: How many times to repeat individual elements of x before moving to the next one.
• length.out: Forces the final output to be exactly this length—truncating extra elements or recycling as needed, and it overrides times and each if there's a conflict.

Some quick examples to make this concrete:

• rep(2, 5): Repeat the single element 2 5 times → [1] 2 2 2 2 2
• rep(c(1,2), each=2): Repeat each element twice before moving on → [1] 1 1 2 2
• rep(c(1,2), times=3): Repeat the whole vector 3 times → [1] 1 2 1 2 1 2

2. Why you're seeing .Primitive("rep") in Kaggle #

That extra output is almost certainly because your code block is running two things at once: your rep(2,5) call and a bare reference to the rep function itself.

In R, if you just type rep (no parentheses) and execute it, R returns the function object. Since rep is a low-level built-in function (written in C for speed), it shows up as .Primitive("rep") instead of a regular function definition.

Double-check your Kaggle notebook code block: you might have an extra line that just says rep after your rep(2,5) call, or a typo that's accidentally triggering the function to be evaluated alongside your actual repetition request. Fix that, and the extra output should vanish.

3. What happens when you pass multiple arguments like rep(2,3,4,5) or rep(1,2,3,4,6,8) #

R matches positional arguments to the function's formal parameters in order—so it fills x first, then times, then length.out, then each. Any extra arguments beyond the first four get ignored entirely.

Let's break down your examples:

rep(2,3,4,5) #

This translates to:

rep(x = 2, times = 3, length.out = 4, each = 5)

Here's how R processes it:

1. First, repeat the single element 2 5 times (thanks to each=5) → [2,2,2,2,2]
2. Then repeat that entire vector 3 times → 15 total 2s
3. But length.out=4 forces the final output to only keep the first 4 elements → [1] 2 2 2 2

rep(1,2,3,4,6,8) #

This only uses the first four arguments, so it's equivalent to:

rep(x = 1, times = 2, length.out = 3, each = 4)

Processing steps:

1. Repeat 1 4 times → [1,1,1,1]
2. Repeat that vector 2 times → 8 total 1s
3. Truncate to the length.out=3 requirement → [1] 1 1 1

Pro tip: Using named arguments (like rep(x=2, each=5, length.out=4)) is way clearer than relying on positional order—you'll avoid confusion and bugs as you work with more complex function calls.

内容的提问来源于stack exchange，提问作者hash_includes_what