Code Snippets to streamline your work

Contents

1. Intro
2. A typical use case
3. How snippets work
4. Using snippets
5. Exporting snippets
6. Snippets not working?

Intro

In this post, we’ll look at how to use code snippets to customize your RStudio environment. It’s an easy-to-use productivity feature that can save you from writing a ton of repetitive code.

A typical use case

I often used the CTRL+SHIFT+R hotkey to generate sections in my code. A dialog box would pop-up for you to insert the label for the section, then it would automatically generate a commented string with you desired label and repeated dashes to the width of your margin setting (default 80; see Tools > Global Options > Code > Display). In the editor, it would look like this:

# label ------------------------------------------------------------------------

However, the format of the string is not modifiable. R has native support for sections using either -, =, or #, and these may be visually preferable to users. For instance, a user might prefer having a few characters preceding the label so as to make it more visible alongside roxygen2 blocks (which start with #'). In my last few projects, I just copied and pasted a section label in the format I wanted, then added the label manually, but this was somewhat tedious.

A user-modifiable format for section labels has been suggested before, but hasn’t been implemented yet. Another user was looking for a similar solution to fix errors with knitr, and was pointed towards using code snippets.

How snippets work

Most users have seen code snippets, whether they realize it or not. By default, if you start writing a function, a box pops up beside the cursor to suggest possible elements you might be typing (e.g., functions, variables). You can click the respective element you want, and the editor will auto-complete that element.

For certain functions, there exist built-in snippets that can do more than just complete the function name, but instead will generate a skeleton for its functionality. This can be seen for common commands like if and for, and even for multiple argument functions like vapply. Typing ‘vapply’, then hitting SHIFT+TAB will generate the code skeleton for vapply:

The auto-complete window that pops-up after inputted a recognized command

Pressing SHIFT+TAB will automatically choose the first command on the list

The list of built-in functions can be found in Tools > Global Options > Code > Edit Snippets....

The RStudio default code snippets

This text box is editable, meaning that the user can add on their own code snippets. A basic overview can be found on RStudio support.

Using snippets

Now the explanations are done, back to the original use case. I prefer to have equal signs instead of dashes, and I like to have a few leading equal signs after the # to better separate from text directly below it. Using the ${1:} nomenclature, you could do something like this:

snippet lbl
  	#==== ${1:label} =======================================================
  	${2:}

^{If the code is not working, check the note.}

With my solution, using the $$ operator in the snippet, I can simple type sect-, add my label, click SHIFT+TAB, and it will auto-create my formatted section label to my preferred width (120 characters):

snippet sect-
      `r strtrim(paste("#====",parse(text = "$$"),strrep("=",150)),120)`

#==== label ====================================================================

The big limitation is that you can’t use any SPACE characters in the label. I use this primarily for function names, and separating sections in a function like validation, code, or logic, so it serves sufficiently well until a similar functionality is included with RStudio. However, there may be a solution to this using custom keyboard shortcuts, but I’ll explore that in a future post.

For some of the snippets I use day-to-day, check out here.

Exporting snippets

Do things

Snippets not working?

There’s a bug of some sort with how the snippets are parsed. As I was writing this, If I COPY+PASTE the snippet directly into the Edit Snippets window in RStudio would sometimes cause the snippet not to work. It has something to do with the indentation of the code. How I fixed it was by just deleting the TAB from the COPY+PASTE line, then typing in a replacement TAB, then it would work. Not sure if this is just my RStudio installation or some weird inconsistency with TAB served by my browser, but it’s annoying nonetheless.

As well, the docs say that it does not accept SPACE for indentation, only TAB, in case the snippets was typed in manually instead.