From 97b074509db6b04ffe025c9a7a7b458c904eef89 Mon Sep 17 00:00:00 2001 From: Hadley Wickham Date: Wed, 27 Apr 2022 08:01:00 -0500 Subject: [PATCH] Polishing pipes now that 4.2 is out --- _common.R | 3 ++- workflow-pipes.Rmd | 39 +++++++++++++++++---------------------- 2 files changed, 19 insertions(+), 23 deletions(-) diff --git a/_common.R b/_common.R index fda083a..396f1f4 100644 --- a/_common.R +++ b/_common.R @@ -26,6 +26,7 @@ status <- function(type) { polishing = "should be readable but is currently undergoing final polishing", restructuring = "is undergoing heavy restructuring and may be confusing or incomplete", drafting = "is currently a dumping ground for ideas, and we don't recommend reading it", + complete = "is largely complete", stop("Invalid `type`", call. = FALSE) ) @@ -33,7 +34,7 @@ status <- function(type) { "::: {.rmdnote}\n", "You are reading the work-in-progress second edition of R for Data Science. ", "This chapter ", status, ". ", - "You can find the polished first edition at .\n", + "You can find the complete first edition at .\n", ":::\n" )) } diff --git a/workflow-pipes.Rmd b/workflow-pipes.Rmd index eea595b..7f687c8 100644 --- a/workflow-pipes.Rmd +++ b/workflow-pipes.Rmd @@ -1,14 +1,14 @@ # Workflow: Pipes {#workflow-pipes} ```{r, results = "asis", echo = FALSE} -status("restructuring") +status("complete") ``` The pipe, `|>`, is a powerful tool for clearly expressing a sequence of operations that transform an object. We briefly introduced pipes in the previous chapter but before going too much farther I wanted to give a few more details and discuss, `%>%`, an predecessor to `|>`. To add the pipe to your code, we recommend using the build-in keyboard shortcut Ctrl/Cmd + Shift + M. -You'll need to make one change to your RStudio options to use `|>` instead of `%>%` as shown in Figure \@ref(fig:pipe-options); more `%>%` that next. +You'll need to make one change to your RStudio options to use `|>` instead of `%>%` as shown in Figure \@ref(fig:pipe-options); more on `%>%` shortly. ```{r pipe-options, out.width = NULL, echo = FALSE} #| fig.cap: > @@ -21,7 +21,7 @@ knitr::include_graphics("screenshots/rstudio-pipe-options.png") ## Why use a pipe? -Each individual dplyr function is quite simple so solving complex problems typically require multiple verbs together. +Each individual dplyr verb is quite simple so solving complex problems typically requires combining multiple verbs. For example, the last chapter finished with a moderately complex pipe: ```{r, eval = FALSE} @@ -34,7 +34,7 @@ flights |> ) ``` -Even though this pipe has four steps, it's quite easy to skim because the verbs come at the start of each line: we start with the flights data, then filter, then group, then summarize. +Even though this pipe has four steps, it's easy to skim because the verbs come at the start of each line: we start with the flights data, then filter, then group, then summarize. What would happen if we didn't have the pipe? We could nest each function call inside the previous call: @@ -65,11 +65,11 @@ flights3 <- summarise(flight2, ) ``` -While both of these forms have their place and time, the pipe generally produces code that is easier to read and easier to write. +While both of these forms have their time and place, the pipe generally produces data analysis code that's both easier to write and easier to read. ## magrittr and the `%>%` pipe -If you've been using the tidyverse for a while, you might be more familiar with the `%>%` pipe provided by the **magrittr** package. +If you've been using the tidyverse for a while, you might be familiar with the `%>%` pipe provided by the **magrittr** package. The magrittr package is included in the code the tidyverse, so you can use `%>%` whenever you load the tidyverse: ```{r, message = FALSE} @@ -86,34 +86,29 @@ Firstly, because it's part of base R, it's always available for you to use, even Secondly, `|>` is quite a bit simpler than `%>%`: in the time between the invention of `%>%` in 2014 and the inclusion of `|>` in R 4.1.0 in 2021, we gained a better understanding of the pipe. This allowed the base implementation to jettison infrequently used and less important features. -## Base pipe vs magrittr pipe +## `|>` vs `%>%` While `|>` and `%>%` behave identically for simple cases there are a few important differences. -These are most likely to affect you if you're a long-term `%>%` user who has taken advantage of some of the more advanced features. -But they're good to know about even if you've never used `%>%`, because you're likely to encounter some of them when reading wild-caught code. +These are most likely to affect you if you're a long-term user of `%>%` who has taken advantage of some of the more advanced features. +But they're still good to know about even if you've never used `%>%` because you're likely to encounter some of them when reading wild-caught code. - By default, the pipe passes the object on its left hand side to the first argument of the function on the right-hand side. - `%>%` allows you change the placement a `.` placeholder. + `%>%` allows you change the placement with a `.` placeholder. For example, `x %>% f(1)` is equivalent to `f(x, 1)` but `x %>% f(1, .)` is equivalent to `f(1, x)`. - - R 4.2.0 will bring a `_` as a placeholder to the base pipe, with one additional restriction: the argument has to be named. + R 4.2.0 added a `_` placeholder to the base pipe, with one additional restriction: the argument has to be named. For example, `x |> f(1, y = _)` is equivalent to `f(1, y = x)`. -- The `|>` placeholder is deliberately simple and can't replicate many features of the `%>%` placeholder: you can't pass it to multiple arguments, and it doesn't have any special behavior when the placeholder is used inside another function (i.e. `df %>% split(.$var)` is equivalent to `split(df, df$var)`. - -- You can also use both `.` and `_` on the left-hand side of operators like `$`, `[[`, `[` (which you'll learn about in Chapter \@ref(vectors)): - - ``` r - mtcars %>% .$cyl - mtcars |> _$cyl - ``` +- The `|>` placeholder is deliberately simple and can't replicate many features of the `%>%` placeholder: you can't pass it to multiple arguments, and it doesn't have any special behavior when the placeholder is used inside another function. + For example, `df %>% split(.$var)` is equivalent to `split(df, df$var)` and `df %>% {split(.$x, .$y)}` is equivalent to `split(df$x, df$y)`. + You can use `.` the left-hand side of operators like `$`, `[[`, `[` (which you'll learn about in Chapter \@ref(vectors)), so you can extract a single column from a data frame with (e.g.) `mtcars %>% .$cyl`. + A future version of R may add similar support for `|>` and `_`. For the special case of extracting a column out of a data frame, you can also use `dplyr::pull():` ```{r} mtcars |> pull(cyl) ``` -- `%>%` allowed you to drop the parentheses when calling a function with no other arguments; `|>` always requires the parentheses. +- `%>%` allows you to drop the parentheses when calling a function with no other arguments; `|>` always requires the parentheses. -- `%>%` allowed you to starting a pipe with `.` to create a function rather than immediately executing the pipe; this is not supported by the base pipe. +- `%>%` allows you to start a pipe with `.` to create a function rather than immediately executing the pipe; this is not supported by the base pipe.