Add advanced R programming episode

[mgalland]

Possible ideas:

Writing R functions

• Writing functions: scope, arguments, etc.
• Vectorisation (sapply, lapply, apply)

Functional programming

• purrr map, map2, etc.
• nested data structure = the List Column Workflow
• fitting multiple models at once
• unnesting

Flow of actions in R

• if
• ifelse
• stop