Assume you wrote a large script, used it in your research, and then had to use it again but with few improvements/changes. You can forget what each line of the code is responsible for. That's why leaving notes in code is a good practice. In programming, we call such notes comments.

A comment is a line/part of a line in the code that is not compiled. To make the interpreter understand, starting from where the code must not be compiled, use the hash # sign. For example, let's leave two comments: one in a separate line, and one right to some calculation:

Input:
# Some calculation
11 + 3 # eleven plus three

Output:
[1] 14

As you can see, there will be only the result of 11+3 displayed in the console.

Please note that using comments is not compulsory but is considered good practice for clean and understandable code.

Comments can also be used while testing to make R ignore some lines of code without removing them.