Replace external R style guide
Internally, we've moved to the Tidyverse Style Guide: style.tidyverse.org
The new file for Rguide.md reflects this fact and notes where we differ.
diff --git a/README.md b/README.md
index b8f87fc..581ec2b 100644
--- a/README.md
+++ b/README.md
@@ -39,7 +39,7 @@
[objc]: objcguide.md
[java]: https://google.github.io/styleguide/javaguide.html
[py]: https://google.github.io/styleguide/pyguide.html
-[r]: https://google.github.io/styleguide/Rguide.xml
+[r]: https://google.github.io/styleguide/Rguide.md
[sh]: https://google.github.io/styleguide/shell.xml
[htmlcss]: https://google.github.io/styleguide/htmlcssguide.html
[js]: https://google.github.io/styleguide/jsguide.html
diff --git a/Rguide.md b/Rguide.md
new file mode 100644
index 0000000..de27371
--- /dev/null
+++ b/Rguide.md
@@ -0,0 +1,109 @@
+# Google's R Style Guide
+
+R is a high-level programming language used primarily for statistical computing
+and graphics. The goal of the R Programming Style Guide is to make our R code
+easier to read, share, and verify.
+
+The Google R Style Guide is a fork of the
+[Tidyverse Style Guide](https://style.tidyverse.org/) by Hadley Wickham
+[license](https://creativecommons.org/licenses/by-sa/2.0/). Google modifications
+were developed in collaboration with the internal R user community. The rest of
+this document explains Google's primary differences with the Tidyverse guide,
+and why these differences exist.
+
+## Syntax
+
+### Naming conventions
+
+Google prefers identifying functions with `BigCamelCase` to clearly distinguish
+them from other objects.
+
+```
+# Good
+DoNothing <- function() {
+ return(invisible(NULL))
+}
+```
+
+The names of private functions should begin with a dot. This helps communicate
+both the origin of the function and its intended use.
+
+```
+# Good
+.DoNothingPrivately <- function() {
+ return(invisible(NULL))
+}
+```
+
+We previously recommended naming objects with `dot.case`. We're moving away from
+that, as it creates confusion with S3 methods.
+
+### Don't use attach()
+
+The possibilities for creating errors when using `attach()` are numerous.
+
+## Pipes
+
+### Right-hand assignment
+
+We do not support using right-hand assignment.
+
+```
+# Bad
+iris %>%
+ dplyr::summarize(max_petal = max(Petal.Width)) -> results
+```
+
+This convention differs substantially from practices in other languages and
+makes it harder to see in code where an object is defined. E.g. searching for
+`foo <-` is easier than searching for `foo <-` and `-> foo` (possibly split over
+lines).
+
+### Use explicit returns
+
+Do not rely on R's implicit return feature. It is better to be clear about your
+intent to `return()` an object.
+
+```
+# Good
+AddValues <- function(x, y) {
+ return(x + y)
+}
+
+# Bad
+AddValues <- function(x, y) {
+ x + y
+}
+```
+
+### Qualifying namespaces
+
+Users should explicitly qualify namespaces for all external functions.
+
+```
+# Good
+purrr::map()
+```
+
+We discourage using the `@import` Roxygen tag to bring in all functions into a
+NAMESPACE. Google has a very big R codebase, and importing all functions creates
+too much risk for name collisions.
+
+While there is a small performance penalty for using `::`, it makes it easier to
+understand dependencies in your code. There are some exceptions to this rule.
+
+* Infix functions (`%name%`) always need to be imported.
+* Certain `rlang` pronouns, notably `.data`, need to be imported.
+* Functions from default R packages, including `datasets`, `utils`,
+ `grDevices`, `graphics`, `stats` and `methods`. If needed, you can `@import`
+ the full package.
+
+When importing functions, place the `@importFrom` tag in the Roxygen header
+above the function where the external dependency is used.
+
+## Documentation
+
+### Package-level documentation
+
+All packages should have a package documentation file, in a
+`packagename-package.R` file.
diff --git a/Rguide.xml b/Rguide.xml
deleted file mode 100644
index ef87872..0000000
--- a/Rguide.xml
+++ /dev/null
@@ -1,447 +0,0 @@
-<?xml version="1.0"?>
-<html xmlns="http://www.w3.org/1999/xhtml">
- <head>
- <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"/>
- <link rel="stylesheet" type="text/css" href="styleguide.css"/>
- <title>Google's R Style Guide</title>
- </head>
-
- <body>
-
- <h1>Google's R Style Guide</h1>
-
- <p>
- R is a high-level programming language used primarily for
- statistical computing and graphics. The goal of the R
- Programming Style Guide is to make our R code easier to read,
- share, and verify. The rules below were designed in
- collaboration with the entire R user community at Google.
-
- </p>
-
-
-
-
-
-
- <h2>Summary: R Style Rules</h2>
-
- <ol>
- <li><a href="#filenames">File Names</a>: end in <code>.R</code></li>
- <li><a href="#identifiers">Identifiers</a>: <code>variable.name</code>
- (or <code>variableName</code>),
- <code>FunctionName</code>, <code>kConstantName</code></li>
- <li><a href="#linelength">Line Length</a>: maximum 80 characters</li>
- <li><a href="#indentation">Indentation</a>: two spaces, no tabs</li>
- <li><a href="#spacing">Spacing</a></li>
- <li><a href="#curlybraces">Curly Braces</a>: first on same line, last on
- own line</li>
- <li><a href="#else">else</a>: Surround else with braces </li>
- <li><a href="#assignment">Assignment</a>: use <code><-</code>, not
- <code>=</code></li>
- <li><a href="#semicolons">Semicolons</a>: don't use them</li>
- <li><a href="#generallayout"> General Layout and Ordering</a></li>
- <li><a href="#comments"> Commenting Guidelines</a>: all comments begin
- with <code>#</code> followed by a space; inline comments need two
- spaces before the <code>#</code></li>
- <li><a href="#functiondefinition">Function Definitions and Calls</a></li>
- <li><a href="#functiondocumentation"> Function Documentation</a></li>
- <li><a href="#examplefunction"> Example Function</a></li>
- <li><a href="#todo"> TODO Style</a>: <code>TODO(username)</code></li>
- </ol>
-
- <h2>Summary: R Language Rules</h2>
- <ol>
- <li><a href="#attach"> <code>attach</code></a>: avoid using it</li>
- <li><a href="#functionlanguage"> Functions</a>:
- errors should be raised using <code>stop()</code></li>
- <li><a href="#object"> Objects and Methods</a>: avoid S4 objects and
- methods when possible; never mix S3 and S4 </li>
- </ol>
-
- <h3>Notation and Naming</h3>
-
- <h4 id="filenames">File Names</h4>
- <p>
- File names should end in <code>.R</code> and, of course, be
- meaningful.
- <br/> GOOD: <code>predict_ad_revenue.R</code>
- <br/> BAD: <code><span style="color:red">foo.R</span></code>
- </p>
-
- <h4 id="identifiers">Identifiers</h4>
- <p>
- Don't use underscores ( <code>_</code> ) or hyphens
- ( <code>-</code> ) in identifiers.
- Identifiers should be named according to the following conventions.
- The preferred form for variable names is all lower case
- letters and words separated with dots
- (<code>variable.name</code>), but <code>variableName</code>
- is also accepted;
- function names have initial capital letters and no dots
- (<code>FunctionName</code>);
- constants are named like functions but with an initial
- <code>k</code>.
- </p>
- <ul>
- <li><code>variable.name</code> is preferred, <code>variableName</code> is accepted
- <br/> GOOD: <code>avg.clicks</code>
- <br/> OK: <code>avgClicks</code>
- <br/> BAD: <code><span style="color:red">avg_Clicks</span></code>
- </li>
- <li><code>FunctionName </code>
- <br/> GOOD: <code>CalculateAvgClicks</code>
- <br/> BAD: <code><span style="color:red">calculate_avg_clicks
- </span></code>,
- <code><span style="color:red">calculateAvgClicks</span></code>
- <br/> Make function names verbs.
- <br/><em>Exception: When creating a classed object, the function
- name (constructor) and class should match (e.g., lm).</em></li>
- <li><code>kConstantName </code></li>
- </ul>
-
-
- <h3>Syntax</h3>
-
- <h4 id="linelength">Line Length</h4>
-<p>
- The maximum line length is 80 characters.
-</p>
-
- <h4 id="indentation">Indentation</h4>
- <p>
- When indenting your code, use two spaces. Never use tabs or mix
- tabs and spaces.
- <br/><em>Exception: When a line break occurs inside parentheses,
- align the wrapped line with the first character inside the
- parenthesis.</em>
- </p>
-
- <h4 id="spacing">Spacing</h4>
- <p>
- Place spaces around all binary operators (<code>=</code>,
- <code>+</code>, <code>-</code>, <code><-</code>, etc.).
- <br/><em> Exception: Spaces around <code>=</code>'s are
- optional when passing parameters in a function call.</em>
- </p>
- <p>
- Do not place a space before a comma, but always place one after a
- comma.
- <br/><br/> GOOD:
- </p>
-<pre>tab.prior <- table(df[df$days.from.opt < 0, "campaign.id"])
-total <- sum(x[, 1])
-total <- sum(x[1, ])</pre>
- <p>
- BAD:
- </p>
-<pre><span style="color:red">tab.prior <- table(df[df$days.from.opt<0, "campaign.id"]) # Needs spaces around '<'
-tab.prior <- table(df[df$days.from.opt < 0,"campaign.id"]) # Needs a space after the comma
-tab.prior<- table(df[df$days.from.opt < 0, "campaign.id"]) # Needs a space before <-
-tab.prior<-table(df[df$days.from.opt < 0, "campaign.id"]) # Needs spaces around <-
-total <- sum(x[,1]) # Needs a space after the comma
-total <- sum(x[ ,1]) # Needs a space after the comma, not before</span>
-</pre>
- <p>
- Place a space before left parenthesis, except in a function call.
- </p>
- <p>
- GOOD:
- <br/><code>if (debug)</code>
- </p>
- <p>
- BAD:
- <br/><code><span style="color:red">if(debug)</span></code>
- </p>
- <p>
- Extra spacing (i.e., more than one space in a row) is okay if it
- improves alignment of equals signs or arrows (<code><-</code>).
- </p>
-<pre>plot(x = x.coord,
- y = data.mat[, MakeColName(metric, ptiles[1], "roiOpt")],
- ylim = ylim,
- xlab = "dates",
- ylab = metric,
- main = (paste(metric, " for 3 samples ", sep = "")))
-</pre>
- <p>
- Do not place spaces around code in parentheses or square brackets.
- <br/><em> Exception: Always place a space after a comma.</em>
- </p>
- <p>
- GOOD:</p><pre>if (debug)
-x[1, ]</pre>
- <p>
- BAD:</p><pre><span style="color:red">if ( debug ) # No spaces around debug
-x[1,] # Needs a space after the comma </span></pre>
-
- <h4 id="curlybraces">Curly Braces</h4>
- <p>
- An opening curly brace should never go on its own line; a closing
- curly brace should always go on its own line. You may omit curly
- braces when a block consists of a single statement; however, you
- must <em>consistently</em> either use or not use curly braces for
- single statement blocks.
- </p>
- <pre>
-if (is.null(ylim)) {
- ylim <- c(0, 0.06)
-}</pre>
- <p>
- xor (but not both)
- </p>
- <pre>
-if (is.null(ylim))
- ylim <- c(0, 0.06)</pre>
- <p>
- Always begin the body of a block on a new line.
- </p>
- <p>
- BAD:
- <br/><code><span style="color:red"> if (is.null(ylim))
- ylim <- c(0, 0.06)</span></code>
- <br/><code><span style="color:red"> if (is.null(ylim))
- {ylim <- c(0, 0.06)} </span></code>
- </p>
-
- <h4 id="else">Surround else with braces</h4>
- <p>
- An <code>else</code> statement should always be surrounded on the
- same line by curly braces.</p>
- <pre>
-if (condition) {
- one or more lines
-} else {
- one or more lines
-}
-</pre>
- <p>
- BAD:<br/>
- </p>
- <pre style="color:red">
-if (condition) {
- one or more lines
-}
-else {
- one or more lines
-}
-</pre>
- <p>
- BAD:<br/>
- </p>
- <pre style="color:red">
-if (condition)
- one line
-else
- one line
-</pre>
-
- <h4 id="assignment">Assignment</h4>
- <p>
- Use <code><-</code>, not <code>=</code>, for assignment.
- </p>
- <p>
- GOOD:
- <br/><code> x <- 5 </code>
- </p>
- <p>
- BAD:
- <br/><code><span style="color:red"> x = 5</span></code>
- </p>
- <h4 id="semicolons">Semicolons</h4>
- <p>
- Do not terminate your lines with semicolons or use semicolons to
- put more than one command on the same line. (Semicolons are not
- necessary, and are omitted for consistency with other Google style
- guides.)
- </p>
-
-
- <h3> Organization </h3>
- <h4 id="generallayout">General Layout and Ordering</h4>
- <p>
- If everyone uses the same general ordering, we'll be able to
- read and understand each other's scripts faster and more easily.
- </p>
- <ol>
- <li>Copyright statement comment </li>
- <li>Author comment</li>
- <li>File description comment, including purpose of
- program, inputs, and outputs</li>
- <li><code>source()</code> and <code>library()</code> statements</li>
- <li>Function definitions</li>
- <li>Executed statements, if applicable (e.g.,
- <code> print</code>, <code>plot</code>)</li>
- </ol>
- <p>
- Unit tests should go in a separate file named
- <code>originalfilename_test.R</code>.
- </p>
- <h4 id="comments">Commenting Guidelines</h4>
- <p>
- Comment your code. Entire commented lines should begin with
- <code>#</code> and one space.
- </p>
- <p>
- Short comments can be placed after code preceded by two spaces,
- <code>#</code>, and then one space.
- </p>
-<pre># Create histogram of frequency of campaigns by pct budget spent.
-hist(df$pct.spent,
- breaks = "scott", # method for choosing number of buckets
- main = "Histogram: fraction budget spent by campaignid",
- xlab = "Fraction of budget spent",
- ylab = "Frequency (count of campaignids)")
-</pre>
- <h4 id="functiondefinition">Function Definitions and
- Calls</h4>
- <p>
- Function definitions should first list arguments without default
- values, followed by those with default values.
- </p>
- <p>
- In both function definitions and function calls, multiple
- arguments per line are allowed; line breaks are only allowed
- between assignments.
- <br/>GOOD:
- </p>
-<pre>PredictCTR <- function(query, property, num.days,
- show.plot = TRUE)
-</pre>
- BAD:
-<pre><span style="color:red">PredictCTR <- function(query, property, num.days, show.plot =
- TRUE)
-</span></pre>
- <p> Ideally, unit tests should serve as sample function calls (for
- shared library routines).
- </p>
- <h4 id="functiondocumentation">Function Documentation</h4>
- <p> Functions should contain a comments section immediately below
- the function definition line. These comments should consist of a
- one-sentence description of the function; a list of the function's
- arguments, denoted by <code>Args:</code>, with a description of
- each (including the data type); and a description of the return
- value, denoted by <code>Returns:</code>. The comments should be
- descriptive enough that a caller can use the function without
- reading any of the function's code.
- </p>
-
- <h4 id="examplefunction">Example Function</h4>
-<pre>
-CalculateSampleCovariance <- function(x, y, verbose = TRUE) {
- # Computes the sample covariance between two vectors.
- #
- # Args:
- # x: One of two vectors whose sample covariance is to be calculated.
- # y: The other vector. x and y must have the same length, greater than one,
- # with no missing values.
- # verbose: If TRUE, prints sample covariance; if not, not. Default is TRUE.
- #
- # Returns:
- # The sample covariance between x and y.
- n <- length(x)
- # Error handling
- if (n <= 1 || n != length(y)) {
- stop("Arguments x and y have different lengths: ",
- length(x), " and ", length(y), ".")
- }
- if (TRUE %in% is.na(x) || TRUE %in% is.na(y)) {
- stop(" Arguments x and y must not have missing values.")
- }
- covariance <- var(x, y)
- if (verbose)
- cat("Covariance = ", round(covariance, 4), ".\n", sep = "")
- return(covariance)
-}
-</pre>
-
-<h4 id="todo">TODO Style</h4>
-
-<p>
- Use a consistent style for TODOs throughout your code.
- <br/><code>TODO(username): Explicit description of action to
- be taken</code>
-</p>
-
-
- <h3> Language </h3>
-
- <h4 id="attach">Attach</h4>
- <p> The possibilities for creating errors when using
- <code>attach</code> are numerous. Avoid it.</p>
- <h4 id="functionlanguage">Functions</h4>
- <p> Errors should be raised using <code>stop()</code>.</p>
- <h4 id="object">Objects and Methods</h4>
- <p> The S language has two object systems, S3 and S4, both of which
- are available in R. S3 methods are more interactive and flexible,
- whereas S4 methods are more formal and rigorous. (For an illustration
- of the two systems, see Thomas Lumley's
- "Programmer's Niche: A Simple
- Class, in S3 and S4" in R News 4/1, 2004, pgs. 33 - 36:
- <a href="https://cran.r-project.org/doc/Rnews/Rnews_2004-1.pdf">
- https://cran.r-project.org/doc/Rnews/Rnews_2004-1.pdf</a>.)
- </p>
- <p>Use S3 objects and methods unless there is a strong reason to use
- S4 objects or methods. A primary justification for an S4 object
- would be to use objects directly in C++ code. A primary
- justification for an S4 generic/method would be to dispatch on two
- arguments.
- </p>
- <p>Avoid mixing S3 and S4: S4 methods ignore S3 inheritance and
- vice-versa.
- </p>
-
-
- <h3>Exceptions</h3>
-
-<p>
- The coding conventions described above should be followed, unless
- there is good reason to do otherwise. Exceptions include legacy
- code and modifying third-party code.
-</p>
-
-
-<h3>Parting Words</h3>
-
-<p>
- Use common sense and BE CONSISTENT.
-</p>
- <p>
- If you are editing code, take a few minutes to look at the code around
- you and determine its style. If others use spaces around their
- <code>if </code>
- clauses, you should, too. If their comments have little boxes of stars
- around them, make your comments have little boxes of stars around them,
- too.
- </p>
- <p>
- The point of having style guidelines is to have a common vocabulary of
- coding so people can concentrate on <em>what</em> you are saying,
- rather than on <em>how</em> you are saying it. We present global style
- rules here so people
- know the vocabulary. But local style is also important. If code you add
- to a file looks drastically different from the existing code around it,
- the discontinuity will throw readers out of their rhythm when they go to
- read it. Try to avoid this.
- </p>
-
- <p>
- OK, enough writing about writing code; the code itself is much more
- interesting. Have fun!
- </p>
-
-
- <h3>References</h3>
-
- <p>
- <a href="http://www.maths.lth.se/help/R/RCC/">
- http://www.maths.lth.se/help/R/RCC/</a> - R Coding Conventions
- </p>
- <p>
- <a href="http://ess.r-project.org/">http://ess.r-project.org/</a> - For
- emacs users. This runs R in your emacs and has an emacs mode.
- </p>
-
- </body>
-
-</html>
