Import STAT 33A lecture notes.

Author: nick-ulle

stat33a/lecture/01.27/notes.Rmd

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+---
+title: "Stat 33A - Lecture 1"
+date: January 27, 2020
+output: pdf_document
+---
+
+Lecture notes will usually be posted to bCourses by the end of the day.
+
+Useful links:
+
+* [RWeekly](https://rweekly.org/), news about R
+* [RStudio Cheat Sheets](https://rstudio.com/resources/cheatsheets/)
+
+## Setting Up
+
+R is an interactive language designed for statistical computing.
+
+RStudio (a separate piece of software) is an integrated development
+environment (IDE) for R.
+
+We'll use RStudio in this course. RStudio bundles in R, so you only need to
+install RStudio.
+
+This week's lab will cover setup, but if you want to get ahead, you can download
+and install RStudio Desktop (free edition) from:
+
+  <https://rstudio.com/products/rstudio/download/>
+
+
+## R Expressions
+The commands we type and send to R are called **expressions**:
+```{r}
+2 * 20
+```
+
+
+## The R Prompt
+
+R has a Read-Eval-Print Loop (REPL):
+
+1. Type an expression at the R prompt and hit the enter key.
+2. R reads the expression.
+3. R evaluates the expression to compute a result.
+4. R prints the result in the console.
+5. R loops back to waiting for you to enter an expression.
+
+
+## R Notebooks
+
+In this course, we'll mostly use R Markdown Notebooks rather than using the R
+prompt directly. Most of the lecture notes and assignments will be R Markdown
+Notebooks.
+
+_The notes in this section are provided by RStudio._
+
+This is an [R Markdown](http://rmarkdown.rstudio.com) Notebook. When you execute
+code within the notebook, the results appear beneath the code. 
+
+Try executing this chunk by clicking the *Run* button within the chunk or by
+placing your cursor inside it and pressing *Ctrl+Shift+Enter*. 
+
+```{r}
+2 + 2
+```
+
+Add a new chunk by clicking the *Insert Chunk* button on the toolbar or by
+pressing *Ctrl+Alt+I*.
+```{r}
+
+```
+
+
+When you save the notebook, an HTML file containing the code and output will be
+saved alongside it (click the *Preview* button or press *Ctrl+Shift+K* to
+preview the HTML file).
+
+The preview shows you a rendered HTML copy of the contents of the editor.
+Consequently, unlike *Knit*, *Preview* does not run any R code chunks. Instead,
+the output of the chunk when it was last run in the editor is displayed.
+
+
+## Order of Operations
+Arithmetic in R follows an **order of operations**, similar to the order of
+operations you probably learned in a math class. Operations are computed from
+from top to bottom:
+
+1. Parentheses `( )`
+2. Exponentiation `^`
+3. Multiplication `*` and Division `/`
+4. Addition `+` and Subtraction `-`
+
+You can test this out in the R prompt or notebook to get a feel for it:
+```{r}
+5 * 6 - 3
+```
+
+R has many more operations besides the ones listed above.
+
+You can see R's complete order of operations with the command:
+```{r}
+?Syntax
+```
+We'll learn about some of these operations later on.
+
+
+## Attendance Question
+Go to
+
+    https://www.yellkey.com/could
+
+to answer. You have until approximately 5pm today.
+
+
+## Using Functions, Part 1
+In R (and most programming languages), a **function** is a reusable command that
+computes something.
+
+Again, this idea is similar (but not identical) to the functions you probably
+learned about in math class.
+
+If we want the sine of 3, we can write:
+```{r}
+sin(3)
+```
+When we use a function to compute something, we usually say we "called" the
+function.
+
+
+R has many built in functions for doing math, statistics, and other computing
+tasks.
+```{r}
+sqrt(5)
+```
+
+
+```{r}
+sum(1, 2, 3)
+```
+
+```{r}
+3 + 4
+```
+
+
+## Getting Help
+R has built-in help files!
+
+You can use the `?` command to get help with a specific function:
+```{r}
+?sin
+```
+The `?` command should be your first stop when you learn a new function.
+
+
+To access the help for an arithmetic operator, you need to put the name in
+single or double quotes:
+```{r}
+?"+"
+```
+
+
+Using quotes this way works for ordinary functions as well:
+```{r}
+?"sin"
+```
+
+
+## Strings
+Sometimes we'll need to treat text as data. In programming languages, a sequence
+of characters (usually textual) is called a **string**.
+
+We already saw how to create a string in R: surround characters with single or
+double quotes.
+```{r}
+"hello class"
+```
+Note that the quote at the beginning needs to match the quote at the end.
+
+
+## Variables
+You can save the result of a computation by assigning it to a **variable**. A
+variable is a name for a value.
+
+Use `=` or `<-` to assign a value to a variable:
+```{r}
+x <- 35
+```
+Either is okay, but choose one and be consistent!
+
+
+Variable names can contain letters or numbers, but can't begin with a number:
+```{r}
+ducks4 = 3
+```
+
+We use use variables to:
+* Avoid redundant computations by storing results.
+* Write general expressions, such as `a*x + b`
+* Break code into small steps, so that it's easier to test and understand.
+
+```{r}
+sin(sqrt(2)) + 3 ^ 2
+sqrt2 = sqrt(2)
+sine = sin(sqrt2)
+
+```
+
+
+### Copy-on-Write
+R's variables are **copy-on-write**.
+
+That is, if we assign `x` to `y`:
+```{r}
+x = 3
+y = x
+```
+
+And then change `x`:
+```{r}
+x = 12
+```
+
+Then `y` remains unchanged:
+```{r}
+y
+```
+
+Originally, `x` and `y` referred to the same value in memory.
+
+When we changed `x` (a "write"), R automatically copied the original value so
+that `y` remained the same.
+
+
+## Using Functions, Part 2
+The values we provide as input to a function are called **arguments**. Some
+functions accept exactly one argument:
+```{r}
+tan(3)
+```
+
+Some functions do not accept any arguments at all. For instance, the
+`sessionInfo()` function, which returns information about your R software:
+```{r}
+sessionInfo()
+```
+
+Some functions accept multiple arguments:
+```{r}
+# Comments on code start with '#'
+log(12, 2) # logarithm of 12, using base 2
+```
+
+Some functions accept any number of arguments:
+```{r}
+sum(1, 2, 3.1)
+```
+
+Each argument gets assigned to a specific parameter of the function.

stat33a/lecture/01.27/notes.pdf

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+
+R version 3.6.2 (2019-12-12) -- "Dark and Stormy Night"
+Copyright (C) 2019 The R Foundation for Statistical Computing
+Platform: x86_64-pc-linux-gnu (64-bit)
+
+R is free software and comes with ABSOLUTELY NO WARRANTY.
+You are welcome to redistribute it under certain conditions.
+Type 'license()' or 'licence()' for distribution details.
+
+  Natural language support but running in an English locale
+
+R is a collaborative project with many contributors.
+Type 'contributors()' for more information and
+'citation()' on how to cite R or R packages in publications.
+
+Type 'demo()' for some demos, 'help()' for on-line help, or
+'help.start()' for an HTML browser interface to help.
+Type 'q()' to quit R.
+
+R version 3.6.2 (2019-12-12) -- Dark and Stormy Night
+Type 'citation()', 'contributors()', or 'license()' for more information
+
+Libraries:
+* /home/nick/.config/R/library
+* /usr/lib/R/library
+
+> 3 + 5
+[1] 8
+> 3 - 5
+[1] -2
+> 3 * 2
+[1] 6
+> 4 / 6
+[1] 0.6666667
+> 2 * 20
+[1] 40
+> 5 * 6 - 3
+[1] 27
+> ?Syntax
+> sin(3)
+[1] 0.14112
+> cos(3)
+[1] -0.9899925
+> sqrt(5)
+[1] 2.236068
+> sum(1, 2, 3)
+[1] 6
+> 3 + 4
+[1] 7
+> ?sin
+> ?+
+. 
+
+> ?"+"
+> ?"sin"
+> "hello class"
+[1] "hello class"
+> x = 35
+> x
+[1] 35
+> y
+Error: object 'y' not found
+> 4ducks = 3
+Error: unexpected symbol in "4ducks"
+> ducks4 = 3
+> sin(sqrt(2)) + 3 ^ 2
+[1] 9.987766
+>