Getting Started

.leftcol30[
<center>
<img src="https://github.com/emse-madd-gwu/emse-madd-gwu.github.io/raw/master/images/logo.png" width=250>
</center>
]

### <svg aria-hidden="true" role="img" viewBox="0 0 512 512" style="height:1em;width:1em;vertical-align:-0.125em;margin-left:auto;margin-right:auto;font-size:inherit;fill:white;overflow:visible;position:relative;"><path d="M243.4 2.587C251.4-.8625 260.6-.8625 268.6 2.587L492.6 98.59C506.6 104.6 514.4 119.6 511.3 134.4C508.3 149.3 495.2 159.1 479.1 160V168C479.1 181.3 469.3 192 455.1 192H55.1C42.74 192 31.1 181.3 31.1 168V160C16.81 159.1 3.708 149.3 .6528 134.4C-2.402 119.6 5.429 104.6 19.39 98.59L243.4 2.587zM256 128C273.7 128 288 113.7 288 96C288 78.33 273.7 64 256 64C238.3 64 224 78.33 224 96C224 113.7 238.3 128 256 128zM127.1 416H167.1V224H231.1V416H280V224H344V416H384V224H448V420.3C448.6 420.6 449.2 420.1 449.8 421.4L497.8 453.4C509.5 461.2 514.7 475.8 510.6 489.3C506.5 502.8 494.1 512 480 512H31.1C17.9 512 5.458 502.8 1.372 489.3C-2.715 475.8 2.515 461.2 14.25 453.4L62.25 421.4C62.82 420.1 63.41 420.6 63.1 420.3V224H127.1V416z"/></svg> EMSE 6035: Marketing Analytics for Design Decisions
### <svg aria-hidden="true" role="img" viewBox="0 0 448 512" style="height:1em;width:0.88em;vertical-align:-0.125em;margin-left:auto;margin-right:auto;font-size:inherit;fill:white;overflow:visible;position:relative;"><path d="M224 256c70.7 0 128-57.31 128-128s-57.3-128-128-128C153.3 0 96 57.31 96 128S153.3 256 224 256zM274.7 304H173.3C77.61 304 0 381.6 0 477.3c0 19.14 15.52 34.67 34.66 34.67h378.7C432.5 512 448 496.5 448 477.3C448 381.6 370.4 304 274.7 304z"/></svg> John Paul Helveston
### <svg aria-hidden="true" role="img" viewBox="0 0 448 512" style="height:1em;width:0.88em;vertical-align:-0.125em;margin-left:auto;margin-right:auto;font-size:inherit;fill:white;overflow:visible;position:relative;"><path d="M96 32C96 14.33 110.3 0 128 0C145.7 0 160 14.33 160 32V64H288V32C288 14.33 302.3 0 320 0C337.7 0 352 14.33 352 32V64H400C426.5 64 448 85.49 448 112V160H0V112C0 85.49 21.49 64 48 64H96V32zM448 464C448 490.5 426.5 512 400 512H48C21.49 512 0 490.5 0 464V192H448V464z"/></svg> August 31, 2022
]

---

# Week 1: .fancy[Getting Started]

### 1. Course orientation
### 2. Intro to conjoint analysis
### 3. Introductions

### BREAK: Teaming

### 4. Getting started with R & RStudio

---

# Week 1: .fancy[Getting Started]

### 1. .orange[Course orientation]
### 2. Intro to conjoint analysis
### 3. Introductions

### BREAK: Teaming

### 4. Getting started with R & RStudio

---

# Meet your instructor!

]]

### John Paul Helveston, Ph.D.

Assistant Professor, Engineering Management & Systems Engineering

- 2016-2018 Postdoc at [Institute for Sustainable Energy](https://www.bu.edu/ise/), Boston University
- 2016 PhD in Engineering & Public Policy at Carnegie Mellon University
- 2015 MS in Engineering & Public Policy at Carnegie Mellon University
- 2010 BS in Engineering Science & Mechanics at Virginia Tech
- Website: [www.jhelvy.com](http://www.jhelvy.com/)

]]

---

# <svg aria-hidden="true" role="img" viewBox="0 0 512 512" style="height:1em;width:1em;vertical-align:-0.125em;margin-left:auto;margin-right:auto;font-size:inherit;fill:currentColor;overflow:visible;position:relative;"><path d="M331.8 224.1c28.29 0 54.88 10.99 74.86 30.97l19.59 19.59c40.01-17.74 71.25-53.3 81.62-96.65c5.725-23.92 5.34-47.08 .2148-68.4c-2.613-10.88-16.43-14.51-24.34-6.604l-68.9 68.9h-75.6V97.2l68.9-68.9c7.912-7.912 4.275-21.73-6.604-24.34c-21.32-5.125-44.48-5.51-68.4 .2148c-55.3 13.23-98.39 60.22-107.2 116.4C224.5 128.9 224.2 137 224.3 145l82.78 82.86C315.2 225.1 323.5 224.1 331.8 224.1zM384 278.6c-23.16-23.16-57.57-27.57-85.39-13.9L191.1 158L191.1 95.99l-127.1-95.99L0 63.1l96 127.1l62.04 .0077l106.7 106.6c-13.67 27.82-9.251 62.23 13.91 85.39l117 117.1c14.62 14.5 38.21 14.5 52.71-.0016l52.75-52.75c14.5-14.5 14.5-38.08-.0016-52.71L384 278.6zM227.9 307L168.7 247.9l-148.9 148.9c-26.37 26.37-26.37 69.08 0 95.45C32.96 505.4 50.21 512 67.5 512s34.54-6.592 47.72-19.78l119.1-119.1C225.5 352.3 222.6 329.4 227.9 307zM64 472c-13.25 0-24-10.75-24-24c0-13.26 10.75-24 24-24S88 434.7 88 448C88 461.3 77.25 472 64 472z"/></svg> Tools

<br>

## <svg aria-hidden="true" role="img" viewBox="0 0 512 512" style="height:1em;width:1em;vertical-align:-0.125em;margin-left:auto;margin-right:auto;font-size:inherit;fill:currentColor;overflow:visible;position:relative;"><path d="M352 256C352 278.2 350.8 299.6 348.7 320H163.3C161.2 299.6 159.1 278.2 159.1 256C159.1 233.8 161.2 212.4 163.3 192H348.7C350.8 212.4 352 233.8 352 256zM503.9 192C509.2 212.5 512 233.9 512 256C512 278.1 509.2 299.5 503.9 320H380.8C382.9 299.4 384 277.1 384 256C384 234 382.9 212.6 380.8 192H503.9zM493.4 160H376.7C366.7 96.14 346.9 42.62 321.4 8.442C399.8 29.09 463.4 85.94 493.4 160zM344.3 160H167.7C173.8 123.6 183.2 91.38 194.7 65.35C205.2 41.74 216.9 24.61 228.2 13.81C239.4 3.178 248.7 0 256 0C263.3 0 272.6 3.178 283.8 13.81C295.1 24.61 306.8 41.74 317.3 65.35C328.8 91.38 338.2 123.6 344.3 160H344.3zM18.61 160C48.59 85.94 112.2 29.09 190.6 8.442C165.1 42.62 145.3 96.14 135.3 160H18.61zM131.2 192C129.1 212.6 127.1 234 127.1 256C127.1 277.1 129.1 299.4 131.2 320H8.065C2.8 299.5 0 278.1 0 256C0 233.9 2.8 212.5 8.065 192H131.2zM194.7 446.6C183.2 420.6 173.8 388.4 167.7 352H344.3C338.2 388.4 328.8 420.6 317.3 446.6C306.8 470.3 295.1 487.4 283.8 498.2C272.6 508.8 263.3 512 255.1 512C248.7 512 239.4 508.8 228.2 498.2C216.9 487.4 205.2 470.3 194.7 446.6H194.7zM190.6 503.6C112.2 482.9 48.59 426.1 18.61 352H135.3C145.3 415.9 165.1 469.4 190.6 503.6V503.6zM321.4 503.6C346.9 469.4 366.7 415.9 376.7 352H493.4C463.4 426.1 399.8 482.9 321.4 503.6V503.6z"/></svg> Course website: https://madd.seas.gwu.edu/2022-Fall/

## <svg aria-hidden="true" role="img" viewBox="0 0 448 512" style="height:1em;width:0.88em;vertical-align:-0.125em;margin-left:auto;margin-right:auto;font-size:inherit;fill:currentColor;overflow:visible;position:relative;"><path d="M94.12 315.1c0 25.9-21.16 47.06-47.06 47.06S0 341 0 315.1c0-25.9 21.16-47.06 47.06-47.06h47.06v47.06zm23.72 0c0-25.9 21.16-47.06 47.06-47.06s47.06 21.16 47.06 47.06v117.8c0 25.9-21.16 47.06-47.06 47.06s-47.06-21.16-47.06-47.06V315.1zm47.06-188.1c-25.9 0-47.06-21.16-47.06-47.06S139 32 164.9 32s47.06 21.16 47.06 47.06v47.06H164.9zm0 23.72c25.9 0 47.06 21.16 47.06 47.06s-21.16 47.06-47.06 47.06H47.06C21.16 243.1 0 222.8 0 196.9s21.16-47.06 47.06-47.06H164.9zm188.1 47.06c0-25.9 21.16-47.06 47.06-47.06 25.9 0 47.06 21.16 47.06 47.06s-21.16 47.06-47.06 47.06h-47.06V196.9zm-23.72 0c0 25.9-21.16 47.06-47.06 47.06-25.9 0-47.06-21.16-47.06-47.06V79.06c0-25.9 21.16-47.06 47.06-47.06 25.9 0 47.06 21.16 47.06 47.06V196.9zM283.1 385.9c25.9 0 47.06 21.16 47.06 47.06 0 25.9-21.16 47.06-47.06 47.06-25.9 0-47.06-21.16-47.06-47.06v-47.06h47.06zm0-23.72c-25.9 0-47.06-21.16-47.06-47.06 0-25.9 21.16-47.06 47.06-47.06h117.8c25.9 0 47.06 21.16 47.06 47.06 0 25.9-21.16 47.06-47.06 47.06H283.1z"/></svg> Course slack: https://emse-madd-f22.slack.com

## <svg aria-hidden="true" role="img" viewBox="0 0 581 512" style="height:1em;width:1.13em;vertical-align:-0.125em;margin-left:auto;margin-right:auto;font-size:inherit;fill:currentColor;overflow:visible;position:relative;"><path d="M581 226.6C581 119.1 450.9 32 290.5 32S0 119.1 0 226.6C0 322.4 103.3 402 239.4 418.1V480h99.1v-61.5c24.3-2.7 47.6-7.4 69.4-13.9L448 480h112l-67.4-113.7c54.5-35.4 88.4-84.9 88.4-139.7zm-466.8 14.5c0-73.5 98.9-133 220.8-133s211.9 40.7 211.9 133c0 50.1-26.5 85-70.3 106.4-2.4-1.6-4.7-2.9-6.4-3.7-10.2-5.2-27.8-10.5-27.8-10.5s86.6-6.4 86.6-92.7-90.6-87.9-90.6-87.9h-199V361c-74.1-21.5-125.2-67.1-125.2-119.9zm225.1 38.3v-55.6c57.8 0 87.8-6.8 87.8 27.3 0 36.5-38.2 28.3-87.8 28.3zm-.9 72.5H365c10.8 0 18.9 11.7 24 19.2-16.1 1.9-33 2.8-50.6 2.9v-22.1z"/></svg> & RStudio: [Course Software Page](https://madd.seas.gwu.edu/2022-Fall/help/course-software.html)

---

# Why <svg aria-hidden="true" role="img" viewBox="0 0 581 512" style="height:1em;width:1.13em;vertical-align:-0.125em;margin-left:auto;margin-right:auto;font-size:inherit;fill:currentColor;overflow:visible;position:relative;"><path d="M581 226.6C581 119.1 450.9 32 290.5 32S0 119.1 0 226.6C0 322.4 103.3 402 239.4 418.1V480h99.1v-61.5c24.3-2.7 47.6-7.4 69.4-13.9L448 480h112l-67.4-113.7c54.5-35.4 88.4-84.9 88.4-139.7zm-466.8 14.5c0-73.5 98.9-133 220.8-133s211.9 40.7 211.9 133c0 50.1-26.5 85-70.3 106.4-2.4-1.6-4.7-2.9-6.4-3.7-10.2-5.2-27.8-10.5-27.8-10.5s86.6-6.4 86.6-92.7-90.6-87.9-90.6-87.9h-199V361c-74.1-21.5-125.2-67.1-125.2-119.9zm225.1 38.3v-55.6c57.8 0 87.8-6.8 87.8 27.3 0 36.5-38.2 28.3-87.8 28.3zm-.9 72.5H365c10.8 0 18.9 11.7 24 19.2-16.1 1.9-33 2.8-50.6 2.9v-22.1z"/></svg>?

---

# Learning Objectives

### After this class, you will know how to...

- ### ...work with data in <svg aria-hidden="true" role="img" viewBox="0 0 581 512" style="height:1em;width:1.13em;vertical-align:-0.125em;margin-left:auto;margin-right:auto;font-size:inherit;fill:currentColor;overflow:visible;position:relative;"><path d="M581 226.6C581 119.1 450.9 32 290.5 32S0 119.1 0 226.6C0 322.4 103.3 402 239.4 418.1V480h99.1v-61.5c24.3-2.7 47.6-7.4 69.4-13.9L448 480h112l-67.4-113.7c54.5-35.4 88.4-84.9 88.4-139.7zm-466.8 14.5c0-73.5 98.9-133 220.8-133s211.9 40.7 211.9 133c0 50.1-26.5 85-70.3 106.4-2.4-1.6-4.7-2.9-6.4-3.7-10.2-5.2-27.8-10.5-27.8-10.5s86.6-6.4 86.6-92.7-90.6-87.9-90.6-87.9h-199V361c-74.1-21.5-125.2-67.1-125.2-119.9zm225.1 38.3v-55.6c57.8 0 87.8-6.8 87.8 27.3 0 36.5-38.2 28.3-87.8 28.3zm-.9 72.5H365c10.8 0 18.9 11.7 24 19.2-16.1 1.9-33 2.8-50.6 2.9v-22.1z"/></svg>
- ### ...design effective surveys to get rich data
- ### ...analyze consumer choice data to model consumer preferences
- ### ...design effective charts to communicate insights

---

# Course prerequisites

### This course requires prior exposure to:

- ### Probability theory
- ### Multivariable calculus
- ### Linear algebra
- ### Regression
]

### **Not sure?**

### Take [this self assessment](https://madd.seas.gwu.edu/2022-Fall/hw/0-self-assessment.html)

]

---

# Reflections (27% of grade)

### Do some readings, recorded lectures, practice problems

### Write a short reflection

---

# **Quizzes** (8% of grade)

> **Why quiz at all?** The "retrieval effect" - basically, you have to _practice_ remembering things, otherwise your brain won't remember them (see the book ["Make It Stick: The Science of Successful Learning"](https://www.hup.harvard.edu/catalog.php?isbn=9780674729018))

---

# Exam (10% of grade)

### Take home exam, 2nd to last week of class

### We'll go over exam solutions on last day of class

---

# [Semester Project](https://madd.seas.gwu.edu/2022-Fall/project/0-overview.html) (46% of grade)

### Teams of 3-4 students

### Goals:

- Assess market viability of a new technology or design
- Recommend best design choices for target market or application

]

### Key deliverables:

Item                  | Weight | Due
----------------------|--------|-------------------------------------
Proposal              | 6 %    | 9/26
Survey Plan           | 4 %    | 10/05
Pilot Survey          | 4 %    | 10/15
Pilot Analysis        | 8 %    | 11/07
Final Survey          | 5 %    | 11/21
Final Analysis Report | 14 %   | 12/13
Final Presentation    | 8 %    | 12/15

]

---

background-color: #FFF

# .center[Grades]

---

# .center[Grades]

Item                  | Weight | Notes
----------------------|--------|-------------------------------------
Reflections           | 27 %   | Weekly assignment (9 x 3%)
Quizzes               | 12 %   | 5 quizzes, lowest dropped
Project Proposal      | 7 %    | Teams of 3-4 students
Survey Plan           | 4 %    |
Pilot Survey          | 4 %    |
Pilot Analysis        | 9 %    |
Final Survey          | 5 %    |
Final Analysis Report | 14 %   |
Final Presentation    | 8 %    |
Final Exam            | 10 %   | Take home exam

---

# Course policies

- ## BE NICE
- ## BE HONEST
- ## DON'T CHEAT

]

## .center[Copying is good, stealing is bad]

> "Plagiarism is trying to pass someone else's work off as your own. Copying is about reverse-engineering."
>
> .right[-- Austin Kleon, from [Steal Like An Artist](https://austinkleon.com/steal/)&ensp;]

]

---

# Late submissions

## - **5** late days - use them anytime, no questions asked
## - No more than **2** late days on any one assignment
## - Contact me for special cases

---

# How to succeed in this class

## <svg aria-hidden="true" role="img" viewBox="0 0 512 512" style="height:1em;width:1em;vertical-align:-0.125em;margin-left:auto;margin-right:auto;font-size:inherit;fill:currentColor;overflow:visible;position:relative;"><path d="M492.7 42.75C517.7 67.74 517.7 108.3 492.7 133.3L436.3 189.7L322.3 75.72L378.7 19.32C403.7-5.678 444.3-5.678 469.3 19.32L492.7 42.75zM44.89 353.2L299.7 98.34L413.7 212.3L158.8 467.1C152.1 473.8 143.8 478.7 134.6 481.4L30.59 511.1C22.21 513.5 13.19 511.1 7.03 504.1C.8669 498.8-1.47 489.8 .9242 481.4L30.65 377.4C33.26 368.2 38.16 359.9 44.89 353.2zM249.4 103.4L103.4 249.4L16 161.9C-2.745 143.2-2.745 112.8 16 94.06L94.06 16C112.8-2.745 143.2-2.745 161.9 16L181.7 35.76C181.4 36.05 181 36.36 180.7 36.69L116.7 100.7C110.4 106.9 110.4 117.1 116.7 123.3C122.9 129.6 133.1 129.6 139.3 123.3L203.3 59.31C203.6 58.99 203.1 58.65 204.2 58.3L249.4 103.4zM453.7 307.8C453.4 308 453 308.4 452.7 308.7L388.7 372.7C382.4 378.9 382.4 389.1 388.7 395.3C394.9 401.6 405.1 401.6 411.3 395.3L475.3 331.3C475.6 330.1 475.1 330.6 476.2 330.3L496 350.1C514.7 368.8 514.7 399.2 496 417.9L417.9 496C399.2 514.7 368.8 514.7 350.1 496L262.6 408.6L408.6 262.6L453.7 307.8z"/></svg> Start assignments early and **read carefully**!

## <svg aria-hidden="true" role="img" viewBox="0 0 640 512" style="height:1em;width:1.25em;vertical-align:-0.125em;margin-left:auto;margin-right:auto;font-size:inherit;fill:currentColor;overflow:visible;position:relative;"><path d="M128 95.1c26.5 0 47.1-21.5 47.1-47.1S154.5 0 128 0S80.01 21.5 80.01 47.1S101.5 95.1 128 95.1zM511.1 95.1c26.5 0 47.1-21.5 47.1-47.1S538.5 0 511.1 0c-26.5 0-48 21.5-48 47.1S485.5 95.1 511.1 95.1zM603.5 258.3l-18.5-80.13c-4.625-20-18.62-36.88-37.5-44.88c-18.5-8-38.1-6.75-56.12 3.25c-22.62 13.38-39.62 34.5-48.12 59.38l-11.25 33.88l-15.1 10.25L415.1 144c0-8.75-7.25-16-16-16H240c-8.75 0-16 7.25-16 16L224 239.1l-16.12-10.25l-11.25-33.88c-8.375-25-25.38-46-48.12-59.38c-17.25-10-37.63-11.25-56.12-3.25c-18.88 8-32.88 24.88-37.5 44.88l-18.37 80.13c-4.625 20 .7506 41.25 14.37 56.75l67.25 75.88l10.12 92.63C130 499.8 143.8 512 160 512c1.25 0 2.25-.125 3.5-.25c17.62-1.875 30.25-17.62 28.25-35.25l-10-92.75c-1.5-13-7-25.12-15.62-35l-43.37-49l17.62-70.38l6.876 20.38c4 12.5 11.87 23.5 24.5 32.63l51 32.5c4.623 2.875 12.12 4.625 17.25 5h159.1c5.125-.375 12.62-2.125 17.25-5l51-32.5c12.62-9.125 20.5-20 24.5-32.63l6.875-20.38l17.63 70.38l-43.37 49c-8.625 9.875-14.12 22-15.62 35l-10 92.75c-2 17.62 10.75 33.38 28.25 35.25C477.7 511.9 478.7 512 479.1 512c16.12 0 29.1-12.12 31.75-28.5l10.12-92.63L589.1 315C602.7 299.5 608.1 278.3 603.5 258.3zM46.26 358.1l-44 110c-6.5 16.38 1.5 35 17.88 41.63c16.75 6.5 35.12-1.75 41.62-17.88l27.62-69.13l-2-18.25L46.26 358.1zM637.7 468.1l-43.1-110l-41.13 46.38l-2 18.25l27.62 69.13C583.2 504.4 595.2 512 607.1 512c3.998 0 7.998-.75 11.87-2.25C636.2 503.1 644.2 484.5 637.7 468.1z"/></svg> Ask for help!

---

# [Getting Help](https://madd.seas.gwu.edu/2022-Fall/help/getting-help.html)

- Mondays from 8:00-5:00pm
- Tuesday from 1:00-5:00pm
- Thursdays from 12:00-5:00pm

---

# Week 1: .fancy[Getting Started]

### 1. Course orientation
### 2. .orange[Intro to conjoint analysis]
### 3. Introductions

### BREAK: Teaming

### 4. Getting started with R & RStudio

---

## We want to answers to questions like...

<br>

### - Higher prices decrease demand, but by how much?

### - How much more is a consumer willing to pay for increased performance in X?

### - How will my product compete against competitors in the market?

## **Answers depend on knowing what people want**

---

## Directly asking people what they want isn't always helpful

### (People want everything)

---

## Which feature do you care more about?

## .center[Battery Life?]

]

## .center[Brand?]

]

## .center[Signal quality?]

]

---

## **Conjoint approach**:<br>Use consumer choice data to model preferences

---

### .center[Use random utility framework to predict probability of choosing phone _j_]

<br>

### 1. `$u_j = \beta_1\mathrm{price}_j + \beta_2\mathrm{brand}_j + \beta_3\mathrm{battery}_j + \beta_4\mathrm{signal}_j + \varepsilon_j$`

### 2. Assume `$\varepsilon_j \sim$` iid extreme value

### 3. Probability of choosing phone _j_: `$P_j = \frac{e^{\beta'x_j}}{\sum_k^J e^{\beta'x_k}}$`

### 4. Estimate `$\beta_1$`, `$\beta_2$`, `$\beta_3$`, `$\beta_4$` by minimizing `$-L = - \sum_n^N \sum_j^J y_{nj} \ln P_{nj}$`

---

## **Willingness to Pay**

<br>

## `$u_j = \beta'x_j + \alpha p_j + \varepsilon_j$`

## `$\omega = \frac{\beta}{-\alpha}$`

]]

## **Make predictions**

### `$P_j = \frac{e^{\hat{\beta}'x_j}}{\sum_k^J e^{\hat{\beta}'x_k}}$`

]

---

# Example: _Pocket Charge_

## A Flexible, Portable Solar Charger

---

---

### Example survey choice question

---

---

# Your project starts now!

# [View project Ideas](https://docs.google.com/presentation/d/1Q9f68tm4JWdi2MdSozqXgYtxrGr6VKqO/edit?usp=sharing)

---

# Week 1: .fancy[Getting Started]

### 1. Course orientation
### 2. Intro to conjoint analysis
### 3. .orange[Introductions]

### BREAK: Teaming

### 4. Getting started with R & RStudio

---

# Introduce yourself

## - Preferred name
## - Degree program
## - Prior experience
## - What do you hope to gain from this class?
## - Project interests?

---

# Break: Teaming

---

# Week 1: .fancy[Getting Started]

### 1. Course orientation
### 2. Intro to conjoint analysis
### 3. Introductions

### BREAK: Teaming

### 4. .orange[Getting started with R & RStudio]

---

# RStudio Orientation

]

- Know the boxes
- Customize the layout
- Customize the look
- [Extra themes](https://github.com/gadenbuie/rsthemes)

]

---

# Open `intro-to-R.R` file and follow along

---

# View prior code in history pane

# Use "up" arrow see previous code

---

# Staying organized

## 1) Save your code in .R files

> ### &zwj;File > New File > R Script

## 2) Keep work in R Project files

> ### File > New Project...

---

## Your turn

### A. Practice getting organized

1. Open RStudio and create a new R project called `week1`.
2. Create a new R script and save it as `practice.R`.
3. Open the `practice.R` file and write your answers to these questions in it.

]]

### B. Creating & working with objects

1). Create objects to store the values in this table:

| City              | Area (sq. mi.) | Population (thousands) |
|-------------------|----------------|------------------------|
| San Francisco, CA | 47             | 884                    |
| Chicago, IL       | 228            | 2,716                  |
| Washington, DC    | 61             | 694                    |

2) Using the objects you created, answer the following questions:

- Which city has the highest density?
  - How many _more_ people would need to live in DC for it to have the same population density as San Francisco?

]]

---

# >15,000 [packages](https://cran.r-project.org/web/packages/available_packages_by_name.html) on the [CRAN](https://cran.r-project.org/)

---

# Installing packages

### `install.packages("packagename")`
### (The package name **must** be in quotes)

```r
install.packages("packagename") # This works
install.packages(packagename)   # This doesn't work
```

### **You only need to install a package once!**

---

# Loading packages

### `library(packagename)`: Loads all the functions in a package
### (The package name _doesn't_ need to be in quotes)

```r
library("packagename") # This works
library(packagename)   # This also works
```

### **You need to _load_ the package every time you use it!**

---

background-color: #fff
class: center

# Installing vs. Loading

---

## Example: **wikifacts**

Install the [Wikifacts](https://github.com/keithmcnulty/wikifacts) package, by Keith McNulty:

```r
install.packages("wikifacts")
```

Load the package:

```r
library(wikifacts) # Load the library
```

Use one of the package functions

```r
wiki_randomfact()
```

```
#> [1] "Did you know that on October 29 in 1986 – British prime minister Margaret Thatcher officially opened the M25, one of Britain's busiest motorways. (Courtesy of Wikipedia)"
```

---

## Example: **wikifacts**

Now, restart your RStudio session:
> Session -> Restart R

Try using the package function again:

```r
wiki_randomfact()
```

```
#> Error in wiki_randomfact(): could not find function "wiki_randomfact"
```

---

# Using only _some_ package functions

### You don't always have to load the whole library.

### Functions can be accessed with this pattern:
`packagename::functionname()`

```r
wikifacts::wiki_randomfact()
```

```
#> [1] "Did you know that in response to the Hong Kong government refusing to close its border with mainland China to contain COVID-19, Winnie Yu organized a labour strike among hospital workers in February 2020? (Courtesy of Wikipedia)"
```

---

## If you haven't yet, install [these packages](https://raw.githubusercontent.com/emse-madd-gwu/2022-Fall/main/content/packages.R)

---

# Back `intro-to-R.R` for the rest of class!