Design of everyday functions

1. The DESIGN 
 of EVERYDAY 
 FUNCTIONS Hadley Wickham
 @hadleywickham
 RStudio September 2018
2. Practitioner Programmer
3. Interactive Easily detect & resolve problems Packaged In production You hear your code Things break and people at you Practitioner Programmer
4. Notebook IDE https://yihui.name/en/2018/09/notebook-war/ The First Notebook War Data analyst Engineer
5. Me You Practitioner Programmer
6. Code is a conversation Ambiguity can be tolerated early and often Practitioner Programmer Implicit Explicit
7. Practitioner Programmer Implicit Explicit
8. What makes a good door? https://99percentinvisible.org/article/norman-doors
10. “When you have trouble with things—whether it’s figuring out whether to push or pull a door or the arbitrary vagaries of the modern computer and electronics industries—it’s not your fault. Don't blame yourself: blame the designer...” — Donald A. Norman
11. https://twitter.com/irismwang/status/994349937944158208
12. https://twitter.com/BrockTibert/status/1009543843690278920
13. https://twitter.com/mattfrost/status/768078660200898560
14. https://twitter.com/gshotwell/status/675344503566417921
15. https://twitter.com/PetrelStation/status/1038043993387552768
16. https://twitter.com/NateApathy/status/1030263775205707776
17. https://twitter.com/scottmccain5/status/986275394692272129
18. “Rule of thumb: if you think something is clever and sophisticated, beware — it is probably self-indulgence.” — Donald A. Norman
19. WAT makes a bad function? https://www.destroyallsoftware.com/talks/wat
20. c(factor("a"), factor("b")) What happens when you combine two factors?
21. c(factor("a"), factor("b")) #> [1] 1 1 What happens when you combine two factors? WAT!
22. today <- as.Date("2018-09-18") lunch <- as.POSIXct("2018-09-18 12:00", tz = "Europe/Belgrade") c(today, lunch) What happens when you combine a date and a date-time?
23. today <- as.Date("2018-09-18") lunch <- as.POSIXct("2018-09-18 12:00", tz = "Europe/Belgrade") c(today, lunch) #> [1] "2018-09-18" #> [2] "4210927-01-24" What happens when you combine a date and a date time? WAT!
24. today <- as.Date("2018-09-18") lunch <- as.POSIXct("2018-09-18 12:00", tz = "Europe/Belgrade") c(lunch, today) What happens when you combine a date and a date-time?
25. today <- as.Date("2018-09-18") lunch <- as.POSIXct("2018-09-18 12:00", tz = "Europe/Belgrade") c(lunch, today) #> [1] "2018-09-18 12:00:00 CDT" #> [2] "1969-12-31 22:56:32 CST" What happens if you touch a date-time the wrong way? WAT!
26. lunch <- as.POSIXct("2018-09-18 12:00", tz = "Europe/Belgrade") lunch #> [1] "2018-09-18 12:00:00 CEST" c(lunch) c(NULL, lunch) What happens if you look at a date-time the wrong way?
27. lunch <- as.POSIXct("2018-09-18 12:00", tz = "Europe/Belgrade") lunch #> [1] "2018-09-18 12:00:00 CEST" c(lunch) #> [1] "2018-09-18 05:00:00 CDT" c(NULL, lunch) #> [1] 1537264800 What happens if you look at a date-time the wrong way? WAT! WAT!!
28. What makes a good function? one aspect of ^
29. c(<factor>, <factor>) -> <integer> c(<datetime<tz>>) -> <datetime> c(NULL, <datetime<tz>>) -> <double> Types can give us a high-level overview of a function I’ll put types in angle brackets to make clear that this is not real R code
30. To do that we need to review some foundations Atomic Numeric Logical Integer Double Character
31. c(<logical>, <logical>) -> <logical> c(<logical>, <integer>) -> <integer> c(<logical>, <double>) -> <double> c(<logical>, <character>) -> <character> c(<integer>, <logical>) -> <logical> c(<integer>, <integer>) -> <integer> c(<integer>, <double>) -> <double> c(<integer>, <character>) -> <character> c(<double>, <logical>) -> <double> c(<double>, <integer>) -> <integer> c(<double>, <double>) -> <double> c(<double>, <character>) -> <character> For atomic vectors, the rules are simple
32. For atomic vectors, the rules are simple Logical Integer Double Character Logical logical integer double character Integer integer integer double character Double double double double character Character character character character character
33. For atomic vectors, the rules are simple Logical Integer Double Character Even if you’re never explicitly learned this, I think you internalise it quickly.
34. Unfortunately c() breaks down when we get to S3 vectors Atomic Numeric Logical Integer Double Character factor POSIXct Date S3 vectors
35. Figuring out the rules is the goal of the vctrs package http://vctrs.r-lib.org
36. mutate(<data.frame>) -> <data.frame> filter(<data.frame>) -> <data.frame> select(<data.frame>) -> <data.frame> arrange(<data.frame>) -> <data.frame> summarise(<data.frame>) -> <data.frame> group_by(<data.frame>) -> <grouped_df> The types of the primary dplyr functions are simple
37. if_else(<logical>, <integer>, <integer>) -> <integer> if_else(<logical>, <double>, <double>) -> <double> if_else(<logical>, <integer>, <logical>) -> ??? if_else(<logical>, <integer>, <double>) -> ??? if_else(<logical>, <factor>, <character>) -> ??? if_else(<logical>, <date>, <datetime>) -> ??? But there are a few that are more complex
38. x <- runif(6) if_else(x > 0.5, x, NA) #> Error: `false` must be type double, #> not logical Which leads to this annoyance
39. x <- runif(6) if_else(x > 0.5, x, NA) #> Error: `false` must be type double, #> not logical if_else(x > 5, x, NA_real_) #> [1] NA 0.700 0.557 NA NA NA Which leads to this annoyance You’re currently forced to learn about the “typed” NAs
40. if_else(<logical>, <integer>, <logical>) -> vec_c(<integer>, <logical>) -> <integer> if_else(<logical>, <factor>, <character>) -> vec_c(<factor>, <character>) -> <error> I think I'm starting to see the principles
41. Fin
42. Practitioner Programmer Implicit Explicit Interactive Easily detect & resolve problems Packaged In production Code is a conversation Ambiguity can be tolerated early and often
43. https://adv-r.hadley.nz/vectors-chap.html http://vctrs.r-lib.org https://www.destroyallsoftware.com/talks/wat https://99percentinvisible.org/article/norman-doors WAT! http://bit.ly/everyday-functions