Lab 02 R Basics

MATH-7360 Data Analysis

Announcement

• Remember to accept GitHub organization invites.

Install Git

Now it’s time that we try out Git, the (probably most) popular version control software. Follow instructions on installing Git from Happy Git and GitHub for the useR.

• For windows users, I highly recommend you using the Option 1 so that we are on the same page.

• For mac users, open a terminal window and run command “xcode-select –install” that installs Xcode command line tools with Git for you.

Git-related Yuja videos

Please watch the Yuja recordings on Canvas under misc of this week. You want to learn how to create a Git repository under our GitHub organization. You also want to learn how to submit your homework. These videos are from 2020, don’t forget to correct the course organization name.

Get started with homework

On GitHub.com:

• Obtain Student Developer Pack. (Should be done by now)

• Create a private repository Math-7360-FirstName-LastName on tulane-math-7360-2023.

On your local machine:

• Clone the repository, create develop branch, where you work on solutions.

  # clone the project
  git clone https://github.com/tulane-math-7360-2023/Math-7360-FirstName-LastName.git
  # enter project folder
  cd Math-7360-FirstName-LastName
  # what branches are there?
  git branch
  # create develop branch
  git branch develop
  # switch to the develop branch
  git checkout develop
  # create folder for HW1
  mkdir hw1
  cd hw1
  # let's write solutions
  echo "sample solution" > hw1.Rmd
  echo "some bug" >> hw1.Rmd
  # commit the code
  git add hw1.Rmd
  git commit -m "start working on problem #1"
  # push to remote repo
  git push

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More on types

R has 5 basic or “atomic” classes of objects:

• character

• numeric (real numbers)

• integer

• complex (not used very often)

• logical (True/False)

When working with vectors in R, it is important to remember that a vector can only be composed of one data type.

What happens when you put multiple objects with different type to form a vector?

The answer is coercion (in other words, type conversion).

Coercion means changing the type of an object and it happens by a pre-set order:

logical < integer < numeric < character

When you create a vector from objects with different types, the lower-order ones will be coerced to the highest type by R.

a <- c(1L, "This is a character")

b <- c(TRUE, "Hello World")

c <- c(FALSE, 2)  # what is wrong here?

Question 1 What types do the above vectors hold?

Explicit coercion

Of course you can coerce objects from one class (type) to another. We can do this by using “as.*” functions where * is the class (type) you want to coerce the object into.

# using the same objects a, b, c from the above question
a.logical <- as.logical(a)
a.integer <- as.integer(a)

## Warning: NAs introduced by coercion

a.numeric <- as.numeric(a)

## Warning: NAs introduced by coercion

b.logical <- as.logical(b)
b.integer <- as.integer(b)

## Warning: NAs introduced by coercion

b.numeric <- as.numeric(b)

## Warning: NAs introduced by coercion

c.logical <- as.logical(c)
c.integer <- as.integer(c)
c.numeric <- as.numeric(c)
c.character <- as.character(c)


d <- -5:5
d.logical <- as.logical(d)

Question 2 What do you get after the coercions? Does any one suprise you? Can you figure out why?

Hint: what are the types of each element in the vectors before you explicitly coerce them?

Try arithmetics

OK, now let’s try arithmetics.

Easy, right?

First let’s create a vector \(\mathbf{v} = (969, 971, 972, \dots, 1022, 1023)\) of 54 elements. (Attention, there is no \(970\) in the vector)

# finish the code below
v <- c()

Then, let’s compute the sum \(\sum_{i=1}^{54}2^{v_i}\).

# finish the code below
v.power.sum <- sum()

How about only sum over 53 elements \(\sum_{i=2}^{54}2^{v_i}\) (note that the sum starts from \(v_2\)).

# finish the code below
v.power.sum.53 <- sum()

Now let’s try putting the first element back

v.power.sum.second <- 2^v[1] + sum()

Question 3 Explain what you found.