class: center, middle  <!-- Do not forget to adapt the presentation title in the header! --> <!-- Adjust the presentation to the session. Focus on the challenges, this is not a coding tutorial. Note, to include figures, store the image in the `/docs/assets/images/yyyymmdd/` folder and use the jekyll base.url reference as done in this template or see https://jekyllrb.com/docs/liquid/tags/#links. using the scale attribute , you can adjust the image size. --> <!-- Adjust the day, month --> # 28 MAY 2020 ## INBO coding club <!-- Adjust the room number and name --> Everywhere you wanna be... --- class: center, middle <!-- Create a new badge using Inkscape or other programs based on the assets/images/coding_club_badges.svg file -->  --- class: center, middle <br> versus <br> Let's [solve it](https://blockly.games/maze?lang=en&level=4&skin=0)!<br> [Blockly](https://blockly.games/?lang=en), learning while having fun: for kids ... and adults. For bird lovers, check the [Bird game](https://blockly.games/bird) to learn `if - else` structure. --- class: center, middle ### How to get started? Check the [Each session setup](https://inbo.github.io/coding-club/gettingstarted.html#each-session-setup) to get started. ### First time coding club? Check the [First time setup](https://inbo.github.io/coding-club/gettingstarted.html#first-time-setup) section to setup. --- class: left, middle  <br> No yellow sticky notes online :-( We use hackmd (see next slide) but basic principle doesn't change. --- class: center, middle ### Share your code during the coding session! <!-- Create a new hackmd file and replace this link (twice!) --> Go to https://hackmd.io/-uDJu4xCS6CC7qNtaK2PLQ?both <iframe src="https://hackmd.io/-uDJu4xCS6CC7qNtaK2PLQ?both" height="400px" width="800px"></iframe> --- class: left, middle ### Load the required packages: ```r library(tidyverse) ``` --- class: center, middle # The `for` loop in R No loop has been more used (and abused) by R users than the **for loop**<br>.  --- class: left, middle # Why loops? [DRY principle](https://en.wikipedia.org/wiki/Don%27t_repeat_yourself) ("<strong>D</strong>on't <strong>R</strong>epeat <strong>Y</strong>ourself") <p></p> DRY is the enemy of WET ("write every time", "write everything twice", "we enjoy typing" or "waste everyone's time") --- background-image: url(/assets/images/background_challenge_1.png) class: left, middle # Challenge 1 Download* R script [`20200528/20200528_challenges.R`](https://github.com/inbo/coding-club/blob/master/src/20200528/20200528_challenges.R) in your folder `./src/20200528` Write `for` loops to: 1. Compute the mean of every column in [`swiss`](https://stat.ethz.ch/R-manual/R-devel/library/datasets/html/swiss.html). 2. Determine the type of each column in [`iris`](https://stat.ethz.ch/R-manual/R-devel/library/datasets/html/iris.html). 3. Compute the number of unique values in each column of `iris`. 4. Generate 10 random normals (`rnorm(n = 10)`) from distributions with means of -10, 0, 10, and 100. __Tip__: https://r4ds.had.co.nz/iteration.html#for-loops --- background-image: url(/assets/images/background_challenge_2.png) class: left, middle # Challenge 2 Download* [`20200528/20200528_births_belgium.txt`](https://github.com/inbo/coding-club/blob/master/data/20200528/20200528_births_belgium.txt) in your folder `./data/20200528/`. It contains the number of births per month in Belgium from 1992 to 2019. Based on a [StatBel open dataset](https://statbel.fgov.be/en/open-data/number-births-day). The code in challenge 2 makes a bar plot of the number of births in Belgium per month in 2010 and save it as a png file. How to do the same for every year from 2010 to 2019 without repeating yourself 10 times? <small>* __Note__: check the getting started instructions on [how to download a single file](https://inbo.github.io/coding-club/gettingstarted.html#each-session-setup)</small> --- class: left, middle # INTERMEZZO 1: nested loops What if you put a loop in another loop? Some dummy examples: ```r years <- c(2019:2020) seasons <- c("winter", "spring", "summer", "autumn") for (year in years) { for (season in seasons) { print(paste0("year:",year, ". Season:", season)) } } "year:2019. Season:winter" "year:2019. Season:spring" "year:2019. Season:summer" "year:2019. Season:autumn" "year:2020. Season:winter" "year:2020. Season:spring" "year:2020. Season:summer" "year:2020. Season:autumn" ``` --- class: left, middle # INTERMEZZO 1: nested loops All possible positions on a chessboard ```r columns <- letters[1:8] rows <- 1:8 for (row in rows) { for (column in columns) { print(paste0("Position: ", column, row)) } } "Position: a1" "Position: b1" "Position: c1" "Position: d1" "Position: e1" "Position: f1" "Position: g1" "Position: h1" "Position: a2" ... "Position: f8" "Position: g8" "Position: h8" ``` --- class: left, middle # INTERMEZZO 2: `while` loop When the end of the loop is not known beforehand, but it depends on a condition, then the for-loop cannot help you. You need a <strong>while</strong>-loop. Example: playing dices. Play until you get more than 10 throwing two dices. ```r result <- 0 n <- 0 while (result < 10) { n <- n + 1 # game number dice <- sample(1:6, size = 2, replace = TRUE) result <- sum(dice) print(paste0("Game number: ", n, ". Result: ", result)) } "Game number: 1. Result: 8" "Game number: 2. Result: 3" "Game number: 3. Result: 9" "Game number: 4. Result: 11" ``` Many videogames are actually a big while loop! --- background-image: url(/assets/images/background_challenge_3.png) class: left, middle # Challenge 3. The Fox slot machine <p>The goal of a fox is to reproduce before it dies.</p> <p>The fox dies for sure after 10 years in the wild. But it can die earlier due to poison (one of the possible `foods`) or by an enemy (all `enemies` except `"safe"`).</p> <p>The "fox game" ends when the fox succeeds to reproduce or when it dies.</p> By using the code provided in [`20200528/20200528_challenges.R`](https://github.com/inbo/coding-club/blob/master/src/20200528/20200528_challenges.R) and using loop techniques: 1. simulate the fox life. Does the fox succeed to reproduce? Or does it die before? 2. Extend the game to a population of 10 foxes. How many foxes succeeded to reproduce? <p> --- class: left, middle ## Bonus challenge: back to Blockly <p>Try solving [level 10](https://blockly.games/maze?lang=en&level=10&skin=0).</p>  --- class: left, middle ## Resources - Well-written and complete tutorial: https://r4ds.had.co.nz/iteration.html - Do you want more? A 2018 Coding club edition about loops: https://inbo.github.io/coding-club/sessions/20181023_coding_club_loops.pdf - Challenge solutions: [20200528/20200528_challenge_solutions.R](https://github.com/inbo/coding-club/blob/master/src/20200528/20200528_challenges_solutions.R) - Video recording of the coding club session is available on [INBO's vimeo channel](https://vimeo.com/424029848) --- class: center, middle  <!-- Adjust the room and date --> Room: online session<br> Date: __30/06/2020__, van 10:00 tot 12:00<br> Subject: functional programming with `purrr`. <br>Loops on steroids.<br> (registration announced via DG_useR@inbo.be)