0XX-purrr.Rmd

---
title: "Repeating things with purrr"
author: "Jeff Oliver"
date: "`r format(Sys.time(), '%d %B, %Y')`"
output:
  html_document: default
  pdf_document:
    latex_engine: xelatex
urlcolor: blue
---

[INTRODUCTORY SENTENCE]

#### Learning objectives
1. one
2. two
3. three

## [DESCRIPTION OR MOTIVATION; 2-4 sentences that would be used for an announcement]

***

## Getting started

***

## [TOPIC ONE]

```{r copied-example, eval = FALSE}
# Define the function, here we are pasting two things together, separated by
# sep_arg (by default, a pipe)
myfun <- function(chr_arg = "yz",
                  num_arg = 0.9,
                  sep_arg = "|") {
  cat(chr_arg, ", ", sep_arg, ", ", num_arg, "\n")
  str_out <- paste(chr_arg, num_arg, sep = sep_arg)
  return(str_out)
}

# Check to make sure it works as expected
myfun()

# Now use it on a pair of lists, replacing default values of chr_arg & num_arg
# Start by making up date
chr_list <- list("ab", "cd", "ef")
num_list <- list(0.1, 0.3, 0.5)

# map2 does myfun over each element in chr_list and num_list
purrr::map2(chr_list, num_list, myfun)

# Swap order of sep_arg and num_arg in function definition
mynotfun <- function(chr_arg = "yz",
                     sep_arg = "|",
                     num_arg = 0.9) {
  cat(chr_arg, ", ", sep_arg, ", ", num_arg, "\n")
  str_out <- paste(chr_arg, num_arg, sep = sep_arg)
  return(str_out)
}

# Works fine for default values
mynotfun()

# Doesn't work on map2
purrr::map2(chr_list, num_list, mynotfun)

# Recover functionality by explicitly providing value for sep_arg
purrr::map2(chr_list, num_list, mynotfun, sep_arg = "*")
```

***

## [TOPIC TWO]

***

## Additional resources

+ [resource one](url-one)
+ [resource two](url-two)
+ A [PDF version](https://jcoliver.github.io/learn-r/lesson-name.pdf) of this lesson

***

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Questions?  e-mail me at <a href="mailto:jcoliver@email.arizona.edu">jcoliver@email.arizona.edu</a>.