commit 8b2d993208a8a0ca7c641956eed8d731e75651a6
parent ee21fe0e74db24c30ae1a99151a72484b629796e
Author: Federica Gazzelloni <61802414+Fgazzelloni@users.noreply.github.com>
Date: Wed, 31 Aug 2022 20:00:50 +0200
added chapter 11 and little change in chapter 10 (#25)
Co-authored-by: Jon Harmon <jonthegeek@gmail.com>
Diffstat:
5 files changed, 104 insertions(+), 9 deletions(-)
diff --git a/10_Function_factories.Rmd b/10_Function_factories.Rmd
@@ -495,10 +495,6 @@ rlang::env_unbind(globalenv(), names(funs))
```
-## Conclusion
-
-
-
diff --git a/11_Function_operators.Rmd b/11_Function_operators.Rmd
@@ -2,12 +2,109 @@
**Learning objectives:**
-- THESE ARE NICE TO HAVE BUT NOT ABSOLUTELY NECESSARY
+- define of function operator
+- find existing function operators
+- how to make your own function operator
-## SLIDE 1
-- ADD SLIDES AS SECTIONS (`##`).
-- TRY TO KEEP THEM RELATIVELY SLIDE-LIKE; THESE ARE NOTES, NOT THE BOOK ITSELF.
+
+## Introduction
+
+In this chapter we'll learn how to use **function operator** as a case of **function factories**.
+
+And we'll see a case study about how to download many web pages using a function operator.
+
+
+## Definition and practical examples
+
+
+```{r 10-01, fig.align='center',fig.dim="50%", fig.cap="Credits: 2001-2003 Michael P.Frank (https://slideplayer.com/slide/17666226/)",echo=FALSE}
+
+knitr::include_graphics("images/11-maths_example.png")
+```
+
+
+
+- A **function operator** is a function that takes one (or more) functions as input and returns a function as output
+
+- Function operators are closely related to **function factories**, infact are a particular case which uses a function as an input.
+
+
+These are the two libraries to use for finding function operator examples:
+
+```{r 11-01_1}
+library(purrr)
+library(memoise)
+```
+
+**What do they do?**
+
+Caching errors:
+
+ purrr::safely()
+
+Caching computations: this function is an example of dynamic programming
+
+ memoise::memoise()
+
+
+### Other exsitsting function operators
+
+
+```{r 11-02, echo=FALSE,fig.align='center', fig.cap="Credits: www.nextptr.com"}
+knitr::include_graphics("images/11-function_operators.png")
+```
+
+> purrr comes with three other function operators in a similar vein:
+
+
+ possibly(): returns a default value when there’s an error. It provides no way to tell if an error occured or not, so it’s best reserved for cases when there’s some obvious sentinel value (like NA).
+
+ quietly(): turns output, messages, and warning side-effects into output, message, and warning components of the output.
+
+ auto_browser(): automatically executes browser() inside the function when there’s an error.
+
+
+
+
+## Case study: make your own function operator
+
+
+```{r 11-03,eval=FALSE}
+urls <- c(
+ "adv-r" = "https://adv-r.hadley.nz",
+ "r4ds" = "http://r4ds.had.co.nz/"
+ # and many many more
+)
+path <- paste(tempdir(), names(urls), ".html")
+
+walk2(urls, path, download.file, quiet = TRUE)
+```
+
+
+Here we make a function operator that add a little delay in reading each page:
+
+```{r 11-04}
+delay_by <- function(f, amount) {
+ force(f)
+ force(amount)
+
+ function(...) {
+ Sys.sleep(amount)
+ f(...)
+ }
+}
+system.time(runif(100))
+#> user system elapsed
+#> 0 0 0
+system.time(delay_by(runif, 0.1)(100))
+#> user system elapsed
+#> 0.00 0.00 0.13
+```
+
+```{r 11-05, eval=FALSE}
+walk2(urls, path, delay_by(download.file, 0.1), quiet = TRUE)
+```
## Meeting Videos
diff --git a/DESCRIPTION b/DESCRIPTION
@@ -26,4 +26,6 @@ Imports:
glue,
scales,
ggplot2,
- patchwork
+ patchwork,
+ memoise,
+ purrr
diff --git a/images/11-function_operators.png b/images/11-function_operators.png
Binary files differ.
diff --git a/images/11-maths_example.png b/images/11-maths_example.png
Binary files differ.
