Assignment for EES 3310/5310 Lab #1

January 24, 2022

Assignment for EES 3310/5310 Lab #1

The file lab-01-report.Rmd is a template for the exercises in Lab #1 to use RMarkdown.

The lab is due by 11:59 pm on Wednesday, Feb. 2. For this first lab assignment, you will get full credit will be given for trying, even if your R code doesn’t work or if you get the answers wrong.

Starting next week, labs will also be graded for correctness and for effective use of RMarkdown in writing up and explaining your answers.

In the report, I give a worked example as a model of how to answer problems using RMarkdown.

There are three exercises for undergraduates and four for graduate students.

Instructions:

• Accept the assignment in GitHub Classroom.

• On your web browser, go to the repository for the assignment.

• In RStudio, create a new project, choose “Version Control”. Then choose “Git” and paste the URL for your assignment repository.

• In your RStudio project, use the template “lab-01-report.Rmd” and fill in text and R code to answer the questions. There is a worked example to help you understand what you need to do.

• When you are done, knit your .Rmd file into a .pdf file or a Word (.docx) file.

• Use git to commit your changes (including the edits to lab-01-report.Rmd and the new .pdf or .docx file) to your local git repository. You can do this from the “Git” tab in RStudio.

• Push the changes from your local git repository to GitHub. You can do this using the “Push” button (the green up arrow) in the “Git” tab in RStudio.

• When you are finished with the lab, or have gotten as far as you can go, go to the Brightspace discussion board and post a comment about your experience using these tools (R, RStudio, and Git) to do these exercises.

  Comment about what was clear, what was unclear or difficult, and any ideas you have about what would make it easier to do these kinds of labs in the future.

As you work on these projects, I advise using git to commit changes frequently as you work and push those commits to GitHub.

Formatting Numbers in R

When you use RMarkdown to write reports, it is helpful to be able to format numbers effectively. For this lab and future ones, I have supplied you with a convenient function called format_md, which allows you to take a number in R and format it flexibly to look good in your report.

There are many ways to format numbers in R and using the format_md function is completely optional. It’s there if you find it helpful, but you don’t have to use it if you don’t want to, or if you prefer to use a different way to format numbers.

If you have a variable x that contains a number, you can format it using format_md(x), and you can specify additional arguments to format_md to control exactly how the number gets formatted.

Let’s start by assigning the value of π to x:

x = pi
format_md(x)

## [1] "3.142"

Now, suppose we only want to format the number to only have two additional digits after the initial 3:

format_md(x, digits = 2)

## [1] "3.14"

Here is another example:

format_md(x * 10, digits = 2)

## [1] "31.4"

format_md(x * 100, digits = 4)

## [1] "314.16"

format_md(x, digits = 10)

## [1] "3.1415926536"

We can also format the number using scientific notation:

y = pi * 1000000
format_md(y, digits = 2, format = "scientific")

## [1] "3.14×10^6^"

Or we can format long numbers to put commas separating the thousands, millions, etc:

format_md(y, comma = TRUE)

## [1] "3,141,593"

Different ways to format numbers

If you want to express a number in scientific notation, you can do this, using format_md. In the example below 1E6 is a convenient way to write 10⁶ in R. You can also write 5E10 to write 5 × 10¹⁰, and so forth.

x = pi * 1E6
print(format_md(x, digits = 2, format = "scientific"))

[1] “3.14×10⁶”

When you are writing Markdown text, there are three good ways to express a number in scientific notation: If we want to express 1.23 × 10⁷, we can do this as

1.23 × 10^7^

(note the ^ both before and after the exponent and the ; in ×) or

$1.23 \times 10^{7}$

(note the dollar signs before and after, and the curly braces {} around the exponent) or

`r format_md(1.23E7, digits=2, format = "scientific")`

which produces 1.23×10⁷. Note the backward quotes ` before and after the R expression and the r after the first `, which tells RMarkdown that this is R code it should evaluate; also note that we used the notation 1.23E7 for the number 1.23 × 10⁷ in R.

We can also tell R to put the numbers directly into our text so we don’t have to type them. If we assign a value to the variable x like this

x = 1.23456E7

then later in our text, we can put a formatted number into the middle of our text.

This RMarkdown text

The value of _x_ is `r format_md(x, digits = 2, format = "scientific")` and
the value of pi is `r format_md(pi, digits = 2)`.

becomes the following:

The value of x is 1.23×10⁷ and the value of pi is 3.14.