I don't do R, sorry. But are you sure your code is O(n)? Try posting it following this, and I (or someone else) will take a look at it.

R Completions 81

The Morse code table is preloaded for you as a dictionary, feel free to use it:

Coffeescript/C++/Go/JavaScript/Julia/PHP/Python/Ruby/TypeScript: MORSE_CODE['.--']

^ That dictionary. You're passing '' as a key to it.

No, that's a problem with your code, not a kata issue. You're passing a key to the dictionary that doesn't exist.