Hands-on intro to R

# Hands-on intro to R
## (And maybe some modeling)
### Mathew Kiang
### 1/24/2018

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# Goals for today

1. Everybody has `R`, RStudio, and `deSolve` installed and can run code

2. Go through discrete time models of population and headaches

3. Intro to non-infectious ODE model of headaches

4. Modify an ODE model

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```r
library(deSolve)
```

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class: center, middle, inverse
## Do you have the file from Canvas?
Download via Canvas

Also download from: https://goo.gl/2YDChe

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# Tips

- In `RStudio` your code in the source panel (upper left) and use **CMD+Enter** or **Ctrl+Enter** to run it in the console
    - This allows you to build on old models without deleting your code

- Comment (`#`) your code as you build models (or as Caroline builds them)
    - Trust me, in a week you'll forget why you wrote something some way

- Drawing the model and/or writing the equations first helps
    - A lot

- You will be given boilerplate code
    - Always

- Use `?` to see the arguments for functions

- Use **ALT + -** to quickly make an assignment (<-)

- It'll be ok. We don't expect you to be `R` masters

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# Discrete birth and deaths

- Here is `discrete_births_and_deaths.R` with comments removed:

```r
population <- 1000
time_seq <- 1:500  
birth_rate <- 0.4
death_rate <- 0.4

dat <- NULL
for (t in time_seq) {
    new_population <- population + round(birth_rate*population) - 
        round(death_rate*population)

dat <- rbind(dat, new_population)

population <- new_population
}

plot(dat[, 1], type = "l")
```

- What's happening in this code? Line-by-line.
- What do we expect to see when we plot this code? Why?
- What do you need to do to make the line go up/down?

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# Hands-on / Live coding

- Please form groups with 1-2 other students. Every group should have at least one person who went through the Swirl or SW tutorials.

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class: center, middle, inverse
# That's it.
## Thanks