26 Iteration

Learning objectives:

• Reduce duplication in code by iterating over a pattern using a for loop.
• Modify an object using a for loop.
• Recognize the three basic ways to loop over a vector using a for loop.
• Handle unknown output lengths by using a more complex result and then combining the result after the for loop.
• Handle unknown sequence lengths with a while loop.
• Reduce duplication in code by passing a function as an argument to a function (functional programming).
• Make iteration code easier to read with the map family of functions from {purrr}.
• Make map code faster to type with shortcuts.
• Compare the map family of functions to the base R apply family.
• Deal with errors and other output using the {purrr} adverbs: safely, possibly, and quietly.
• Map over multiple arguments with the map2 family and the pmap family from {purrr}.
• Map over multiple functions with the invoke_map family from {purrr} and its replacements (see ?purrr::invoke_map, “Life cycle”).
• Call a function for its side effects using the walk family of functions from {purrr}.
• Recognize the other iteration functions from {purrr}.